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Volume 101, Issue 10, 15 November 1994

Analysis of the crystal‐field spectra of the actinide tetrafluorides. II. AmF_{4}, CmF_{4}, Cm^{4+}:CeF_{4}, and Bk^{4+}:CeF_{4}
View Description Hide DescriptionWe report a systematic analysis of the crystal‐field spectra of four fluoride compounds containing tetravalent actinide ions. The first part of this work [J. Chem. Phys. 95, 7194 (1991)] provided interpretation of the absorption spectra of UF_{4}, NpF_{4}, and PuF_{4}. To extend our analysis to heavier elements of the series, low‐temperature absorption spectra of AmF_{4} and CmF_{4}, and site selective laser‐induced emission and excitation spectra of Cm^{4+}:CeF_{4} and Bk^{4+}:CeF_{4} were obtained. A model energy level calculation was found to be in good agreement with the experimental results. It is shown that the crystal‐field interaction in combination with spin–orbital coupling results in significant J mixing in the excited states, but ground statewave functions are still relatively pure in J character for the tetravalent actinide ions Am^{4+}, Cm^{4+}, and Bk^{4+}. Trends in the parameters of the effective operator Hamiltonian are compared with those of a Hartree–Fock free‐ion model. Interpretation of the ground‐state splitting of the nominal S‐state ion Bk^{4+} in CeF_{4} and color center formation in AmF_{4} are also discussed.

Matrix isolation study of the interaction of excited neon atoms with CF_{4}. Infrared spectra of CF^{+} _{3} and CF^{−} _{3}
View Description Hide DescriptionWhen a Ne:CF_{4} sample is codeposited at approximately 5 K with a beam of neon atoms that have been excited in a microwavedischarge, the infrared spectrum of the resulting sample shows prominent absorptions of CF_{2} and CF_{3}, as well as a complex absorption pattern between 1650 and 1670 cm^{−1}. Earlier reports of the infrared spectrum of CF^{+} _{3} produced from various CF_{3}X species and trapped in solid argon are consistent with the assignment of this group of absorptions to ν_{3} of CF^{+} _{3}. The prediction of those studies that the ν_{1}+ν_{4} combination band of ^{12}CF^{+} _{3} should lie near 1625 cm^{−1} is confirmed. Supplementary observations on Ne:HCF_{3} and Ne:DCF_{3} samples support these assignments, as well as that of the ν_{2}(a _{2} ^{‘}) fundamental of CF^{+} _{3} at 798.1 cm^{−1}. Ab initio calculations of the structure and vibrational fundamentals of ground‐state CF^{−} _{3} are consistent with the tentative assignment of two infrared absorptions to that species.

Observation of CH A→X, CN B→X, and NH A→X emissions in gas‐phase collisions of fast O(^{3} P) atoms with hydrazines
View Description Hide DescriptionOptical emissions in single‐collision reactions of fast (20 eV laboratory translational energy) O(^{3} P) atoms with hydrazine, methylhydrazine, and 1,1‐dimethylhydrazine have been measured in a crossed‐beams geometry. The emissions were observed in the wavelength range 325–440 nm, and were identified as the CH (A ^{2}Δ→X ^{2}Π_{ r }) (for methylhydrazine), CN (B ^{2}Σ^{+}→X ^{2}Σ^{+}) (for methylhydrazine), and NH (A ^{3}Π→X ^{3}Σ^{−}) transitions (for all three hydrazines). The experimental vibration‐rotation bands were fit to a synthetic spectrum of CH, CN, and NH with given vibrational and rotational temperatures.

Zero kinetic energy, pulsed‐field ionization spectroscopy of hydrogen iodide
View Description Hide DescriptionThe rotationally resolved, zero kinetic energy, pulsed‐field ionization (ZEKE‐PFI) spectrum of the HI^{+} X ^{2}Π_{1/2}, v ^{+}=0 level, obtained by double‐resonance excitation via the HI F ^{1}Δ_{2}, v=0 level, is reported. The rotational and Λ‐doubling constants for the HI^{+} X ^{2}Π_{1/2}, v ^{+}=0 level obtained from the experiment are close to those estimated theoretically by Mank et al. [J. Chem. Phys. 95, 1676 (1991)]. At higher pressures, the dissociative charge transferreaction HI*+HI→HI^{+}+H+I^{−} represents a potentially serious loss mechanism for the high Rydberg states that give rise to the ZEKE‐PFI signal. This result is of more general applicability, because it provides evidence that collisions of the Rydberg electron with neighboring molecules can play a significant role in ZEKE‐PFI experiments.

Ar_{ n }H_{2}O (n=1–14) van der Waals clusters: Size evolution of equilibrium structures
View Description Hide DescriptionSize evolution of the equilibrium structures of Ar_{ n }H_{2}O van der Waals clusters with n=1–14 has been investigated. Pairwise additive intermolecular potential energy surfaces (IPESs) for Ar_{ n }H_{2}O clusters were constructed from the spectroscopically accurate Ar–Ar and anisotropic 3D Ar–H_{2}O potentials. For each cluster size considered, we determined the global minimum of the respective IPES and several other lowest‐lying Ar_{ n }H_{2}O isomeric structures. This was accomplished by using simulated annealing followed by a direct minimization scheme. The minimum‐energy structures of all Ar_{ n }H_{2}O clusters considered in this work are fully solvated; up to n=12, the Ar atoms fill a monolayer around H_{2}O. For n=12, the optimal Ar_{12}H_{2}O structure has the Ar atoms arranged in a highly symmetrical icosahedron, with H_{2}O in its center. The icosahedral Ar_{12}H_{2}O structure is exceptionally stable; the energy gap separating it from the next higher n=12 isomer (289.55 cm^{−1}) exceeds that for any other cluster in this size range. The observed preference for solvated Ar_{ n }H_{2}O structures was carefully analyzed in terms of the relative energetic contributions from Ar–Ar and Ar–H_{2}O interactions. For n≤9, the monolayer, cagelike geometries are favored primarily by providing optimal Ar–H_{2}O interactions, significantly larger than for alternative Ar_{ n }H_{2}O structures. For n≳9, the solvated Ar_{ n }H_{2}O isomers offer the best Ar–Ar packing, in addition to the strongest total Ar–H_{2}O interactions. A detailed comparison was made with the minimum‐energy structures of Ar_{ n }HF clusters, determined by us recently [J. Chem. Phys. 100, 7166 (1994)], revealing interesting differences in the growth patterns of the optimal cluster structures.

Algebraic approach to vibrational spectra of tetrahedral molecules: Application to methane
View Description Hide DescriptionWe present an algebraic approach to describe the vibrational excitations of polyatomic molecules. The model is based on the coupling of anharmonic oscillators and is characterized by combining the strengths of the Lie‐algebraic methods with those of point symmetry techniques. We illustrate the algebraic method for tetrahedral molecules and apply it to the construction of the complete vibrational spectra of methane up to four quanta.

Nonoptical excited state spectroscopy of CF_{3}Cl, CF_{2}Cl_{2}, and CFCl_{3}: Bethe surfaces, and absolute transition probability measurement of preionization‐edge valence and Rydberg transitions by angle‐resolved electron energy loss spectroscopy
View Description Hide DescriptionAbsolute transition probabilities or generalized oscillator strengths (GOSs) of valence‐shell electronic transitions of CF_{3}Cl, CF_{2}Cl_{2}, and CFCl_{3} as functions of energy loss and momentum transfer (or Bethe surfaces) have been determined using angle‐resolved electron energy loss spectroscopy(EELS) at an impact energy of 2.5 keV. Low‐lying electronic excitation features in the energy loss region of 6.8–8.1 eV are observed. Using the results of single‐excitation configuration interaction excited‐state calculations, we show that these excitation features can be attributed predominantly as electronic transitions from the Cl 3p nonbonding (n) orbitals to a C–Cl σ* antibonding orbital (i.e., n→σ* transitions), some of which may lead to dissociation of the C–Cl bond. Moreover, the absolute GOS profiles of these low‐lying excitation features have been determined for the first time. In particular, the GOS profile of the n→σ* feature of CF_{3}Cl at 7.7 eV has been found to have a shape characteristic of a quadrupole transition. On the other hand, the GOS profiles of analogous excitation features for CF_{2}Cl_{2} and CFCl_{3} are found to have more complicated structures. The combined profiles of the GOSs of these n→σ* excitation features in the CF_{4−m }Cl_{ m } (m=1–4) series indicate increased dipole component with the number of chlorine atoms. The possible mechanisms and significance of this trend in the GOSs of these n→σ* transitions have been discussed. Furthermore, the GOS profiles of low‐lying preionization‐edge Rydberg transitions (that originate from the Cl 3p nonbonding orbitals) are also determined, and found to contain not only strong maxima at zero momentum transfer, which are characteristic of predominant dipole‐allowed interactions, but also weak secondary maxima (and minima). The nature of these secondary extrema in the GOS profiles is discussed by considering the spatial overlaps of the initial‐state and final‐state orbital wave functions. Finally, we provide new tentative assignments for other valence‐shell energy loss features of CF_{3}Cl, CF_{2}Cl_{2}, and CFCl_{3} using the ionization potentials and term values reported in the literature.

Signatures of large amplitude motion in a weakly bound complex: High‐resolution IR spectroscopy and quantum calculations for HeCO_{2}
View Description Hide DescriptionThe infrared spectrum of the HeCO_{2} van der Waals molecule is recorded in the region of the CO_{2} ν_{3} asymmetric stretch via direct absorption of a tunable Pb–salt diode laser. HeCO_{2} is formed in a slit jet supersonic expansion; the slit valve and the stagnation gas must be precooled to −35 °C before substantial formation of the complex is observed. Sixty‐six rovibrational transitions are recorded by exciting the ν_{3} asymmetric stretch of the CO_{2}monomer within the complex. Forty‐three of these transitions can be assigned using internally consistent combination differences as a b‐type band of a T‐shaped asymmetric rotor. There are several indications that large amplitude motion is significant in HeCO_{2}, including the poor quality of the fit to an asymmetric rotor model and the large positive inertial defects of Δ=8.54 and 10.98 uÅ^{2} in the ground and excited states, respectively. However, a hindered rotor analysis based on these inertial defects demonstrates that the CO_{2} motion within the complex is far from the free rotor limit. No evidence of predissociation broadening is observed, indicating a lifetime for the complex of τ≳6 ns. Quantum close‐coupling calculations which correctly treat both angular and radial degrees of freedom are carried out on the full 2D HeCO_{2} potential energy surface of Beneventi et al. [J. Chem. Phys. 89, 4671 (1988)]. Comparison of this analysis with the experimental results demonstrates that the theoretical potential is too isotropic in the region of the potential minimum.
Predicted spectra from this model potential, however, indicate that the remaining 17 much weaker HeCO_{2} transitions are due to a ‘‘hot band’’ excitation out of the first intermolecular bending level, lying 9±2 cm^{−1} above the ground state. In sharp contrast to the ground vibrational state of HeCO_{2}, an asymmetric rotor model fails qualitatively to characterize the rotational structure for the lowest excited bend. The simple physical reason for this is confirmed by inspection of the quantum wave functions; in the ground state the He atom is localized near the C atom in a T‐shaped geometry, whereas in any of the excited bending states the He atom is largely delocalized around the CO_{2} molecular framework.

Infrared intensities of liquids. XVII. Infrared refractive indices from 8000 to 350 cm^{−1}, absolute integrated absorption intensities, transition moments, and dipole moment derivatives of methan‐d _{3}‐ol and methanol‐d _{4} at 25 °C
View Description Hide DescriptionThis paper reports absolute infrared absorption intensities of liquids methan‐d _{3}‐ol (CD_{3}OH) and methanol‐d _{4} (CD_{3}OD) at 25 °C between 8000 and 350 cm^{−1}. Measurements were made by multiple attenuated total reflection spectroscopy with the CIRCLE cell, and by transmission spectroscopy with transmission cells fitted with calcium fluoride windows. In both cases, the spectra were converted to infrared real and imaginary refractive indexspectra. The refractive indices obtained by these two methods agreed excellently and were combined to yield an imaginary refractive indexspectrumk(ν̃) between 7244 and 350 cm^{−1} for CD_{3}OH and between 5585 and 350 cm^{−1} for CD_{3}OD. The imaginary refractive indexspectrum was arbitrarily set to zero from 8000 to 7244 cm^{−1} (CD_{3}OH) or 5585 cm^{−1} (CD_{3}OD), where k is always less than 4×10^{−6}, in order that the real refractive index can be calculated below 8000 cm^{−1} by Kramers–Krönig transformation. The results are reported as graphs and tables of the refractive indices between 8000 and 350 cm^{−1}, from which all other infrared properties of the two liquids can be calculated. The estimated accuracy, not precision, of the imaginary refractive index is ±3%, except for ±10%, where k is less than 4×10^{−5}. The estimated accuracy of the real refractive index is better than ±0.5%.
In order to obtain molecular information from the measurements, the spectra of the imaginary polarizability multiplied by wave number ν̃α_{m} ^{‘} were calculated under the assumption of the Lorentz local field. The area under these ν̃α_{m} ^{‘}spectra was separated into the integrated intensities of different vibrations. The magnitudes of the transition moments were calculated from the integrated intensities, and the double harmonic approximation was used to calculate the magnitudes of the dipole moment derivatives of the liquid‐state molecules with respect to the normal coordinates. Dipole moment derivatives with respect to internal coordinates were calculated under the simplest approximations, the validity of which is demonstrated by the experimental data in many cases. The consistency of the dipole moment derivatives with respect to internal coordinates obtained for different isotopomers is shown through their relative rotational corrections. Results are presented for the O–H, O–D, C–H, and C–D stretches; the C–O–H in‐plane bending; and the D–C–O–H and D–C–O–D torsion vibrations.

Molecular rotations and local modes
View Description Hide DescriptionRotational energy level structures of stretching vibrational states have been investigated in the XH_{2}, XH_{3}, and XH_{4} type symmetrical hydrides. Transformations from standard vibration–rotation normal coordinate Hamiltonians are made to internal coordinate representations which explicitly give the terms responsible for rotational coupling between the different local mode states. It is shown that the local mode relations between the vibration–rotation parameters as given by Lehmann [J. Chem. Phys. 95, 2361 (1991)] and by Halonen and Robiette [J. Chem. Phys. 84, 6861 (1986)] make these Hamiltonians diagonal in the local mode basis. The effective vibration–rotation parameters of overtones are then proved to obey the local mode relations closer and closer as the vibrational excitation increases. A simple vibrational model accounts well for the vibrational dependencies of vibration–rotation constants in the case of SiH_{4}, GeH_{4}, and SnH_{4}.

The Raman and vibronic activity of intermolecular vibrations in aromatic‐containing complexes and clusters
View Description Hide DescriptionTheoretical and experimental results pertaining to the excitation of intermolecular vibrations in the Raman and vibronic spectra of aromatic‐containing, weakly bound complexes and clusters are reported. The theoretical analysis of intermolecular Raman activity is based on the assumption that the polarizabilitytensor of a weakly bound species is given by the sum of the polarizabilitytensors of its constituent monomers. The analysis shows that the van der Waals bending fundamentals in aromatic–rare gas complexes may be expected to be strongly Raman active. More generally, it predicts strong Raman activity for intermolecular vibrations that involve the libration or internal rotation of monomer moieties having appreciable permanent polarizabilityanisotropies. The vibronic activity of intermolecular vibrations in aromatic‐rare gas complexes is analyzed under the assumption that every vibronic band gains its strength from an aromatic‐localized transition. It is found that intermolecular vibrational excitations can accompany aromatic‐localized vibronic excitations by the usual Franck–Condon mechanism or by a mechanism dependent on the librational amplitude of the aromatic moiety during the course of the pertinent intermolecular vibration. The latter mechanism can impart appreciable intensity to bands that are forbidden by rigid‐molecule symmetry selection rules. The applicability of such rules is therefore called into question. Finally, experimental spectra of intermolecular transitions, obtained by mass‐selective, ionization‐detected stimulated Raman spectroscopies, are reported for benzene–X (X=Ar, –Ar_{2}, N_{2}, HCl, CO_{2}, and –fluorene), fluorobenzene–Ar and –Kr, aniline–Ar, and fluorene–Ar and –Ar_{2}. The results support the conclusions of the theoretical analyses and provide further evidence for the value of Raman methods in characterizing intermolecular vibrational level structures.

MIE scattering from anisotropic thick spherical shells
View Description Hide DescriptionA theory of the electromagneticscattering from spherical shells composed of radially oriented optically anisotropicscattering elements is presented. The theory is valid for arbitrary shell size and index of refraction but is limited to moderate shell thickness compared to the shell radius. The theory includes the effect of the shell thickness to second order, thereby extending previous work by Lange and Aragón [J. Chem. Phys. 92, 4643, (1990)]. Exact closed form solutions could be obtained for some, but not all of the terms in the expansion. Extensive comparisons with exact numerical computations based on infinite series of non‐integral order Bessel functions are included, as well as comparisons with the exact closed form expressions of the first order theory. The relationship of the second order theory to the Rayleigh–Debye approximation is examined and it is shown that, in contrast to the first order case, there are Mie corrections to the effects of the optical anisotropy on the scattering amplitudes. These results are useful in the interpretation of light scattering experiments from phospholipid vesicle dispersions.

O–H torsional vibrations in the S _{0} and S _{1} states of catechol
View Description Hide DescriptionA spectroscopic study of supersonic jet‐cooled catechol (1,2‐dihydroxybenzene) and its d _{1}‐ and d _{2}‐isotopomers, deuterated at the hydroxy groups, was performed by resonant two‐photon ionization (R2PI) and fluorescence emission techniques, and supplemented by molecular‐beam hole‐burning experiments. The latter prove that one single rotamer of catechol is dominant under molecular beam conditions. The complicated vibrational structure in the S _{0}→S _{1} spectrum from the 0^{0} _{0} band to 400 cm^{−1} above is not due to three different rotamers, as previously thought, but is due to the excitation of a vibrational progression associated mainly with the torsion of the hydroxy groups. The torsional bands are very prominent in the R2PI spectra, but are weak in the emission spectra. Detailed analysis of the torsional bands was based on a fit to the S _{1} and S _{0} state frequencies and the Franck–Condon factors in absorption and emission, using a double‐minimum potential for the S _{1} state and a harmonic potential for the S _{0} state. In the S _{1} state one of the two –O–H torsional mode frequencies is lowered from τ_{2}≊250 to ≊50 cm^{−1}, and the molecule is only quasiplanar with respect to the –O–H torsional coordinates.

Structure, internal mobility, and spectrum of the ammonia dimer: Calculation of the vibration–rotation‐tunneling states
View Description Hide DescriptionWe have obtained a potential for (NH_{3})_{2} by calculating the six‐dimensional vibra‐ tion–rotation‐tunneling (VRT) states from a model potential with some variable parameters, and adjusting some calculated transition frequencies to the observed far‐infrared spectrum. The equilibrium geometry is strongly bent away from a linear hydrogen bonded structure. Equivalent minima with the proton donor and acceptor interchanged are separated by a barrier of only 7 cm^{−1}. The barriers to rotation of the monomers about their C _{3} axes are much higher. The VRT levels from this potential agree to about 0.25 cm^{−1} with all far‐infrared frequencies of (NH_{3})_{2} observed for K=0, ‖K‖=1, and ‖K‖=2 and for all the symmetry species: A _{ i }=ortho–ortho, E _{ i }=para–para, and G=ortho–para. Moreover, the dipole moments and the nuclear quadrupole splittings agree well with the values that are observed for the G states. The potential has been explicitly transformed to the center‐of‐mass coordinates of (ND_{3})_{2} and used to study the effects of the deuteration on the VRT states. The observed decrease of the dipole moment and the (small) changes in the nuclear quadrupole splittings are well reproduced. It follows from our calculations that the ammonia dimer is highly nonrigid and that vibrational averaging effects are essential. Seemingly contradictory effects of this averaging on its properties are the consequence of the different hindered rotor behavior of ortho and paramonomers.

The nature of monomer inversion in the ammonia dimer
View Description Hide DescriptionA model is presented for calculating the splittings due to umbrella inversion of the monomers in (NH_{3})_{2}. Input to the model are the six‐dimensional dimer bound statewave functions for rigid monomers, calculated previously [E. H. T. Olthof, A. van der Avoird, and P. E. S. Wormer, J. Chem. Phys. 101, 8430 (1994)]. This model is based on first‐order (quasi) degenerate perturbation theory and adaptation of the wave functions to the group chain G _{36}⊆G _{72}⊆G _{144}. The umbrella inversion splittings depend sensitively on the intermolecular potential from which the bound statewave functions are obtained. A complete interpretation of the observed splitting pattern [J. G. Loeser, C. A. Schmuttenmaer, R. C. Cohen, M. J. Elrod, D. W. Steyert, R. J. Saykally, R. E. Bumgarner, and G. A. Blake, J. Chem. Phys. 97, 4727 (1992)] and quantitative agreement with the measured splittings, which range over three orders of magnitude, are obtained from the potential that reproduces the far‐infrared spectrum of (NH_{3})_{2} and the dipole moment and nuclear quadrupole splittings of (NH_{3})_{2} and (ND_{3})_{2}. The umbrella inversion splittings of (ND_{3})_{2} are predicted.

Threshold for quasicontinuum absorption and reduced luminescence efficiency in CdSe nanocrystals
View Description Hide DescriptionLuminescence excitation spectra are employed to study the electronic states of CdSenanocrystals ranging in size from 9 to 26 Å radius at 77 K. These studies show that all samples have, in addition to the discrete manifold of quantum confined electronic excitations, a threshold for continuum absorption. Absorption into this continuum results in substantially reduced luminescence efficiency.

Impulsive excitation of coherent vibrational motion ground surface dynamics induced by intense short pulses
View Description Hide DescriptionA framework for understanding impulsively photoinduced vibrational coherent motion on the ground electronic surface is presented. In particular strong resonant excitation to a directly dissociative electronic surface is considered. Three distinct approaches are employed. A two surface Fourier wavepacket method explicitly including the field explores this process in isolated molecules. A coordinate dependent two‐level system is employed to develop a novel analytical approximation to the photoinduced quantum dynamics. The negligible computational requirements make it a powerful interactive tool for reconstructing the impulsive photoexcitation stage. Its analytical nature provides closed form expressions for the photoinduced changes in the material. Finally the full simulation of the process including the solvent effects is carried out by a numerical propagation of the density operator. In all three techniques the excitation field is treated to all orders, allowing an analysis of current experiments using strong fields, resulting in substantial photoconversion. The emerging picture is that the impulsive excitation carves a coherent dynamical ‘‘hole’’ out of the ground surface density. A rigorous definition of the dynamical ‘‘hole’’ is constructed and used to define a measure of its coherence. In particular all photoinduced time dependence in the system can be directly related to the dynamical ‘‘hole.’’ All three techniques are used to simulate the pump probe experiment on the symmetric stretch mode of I _{ 3 } ^{ − } , including electronic and vibrational dephasing.

Laser spectroscopy of molecular ions: The A–X transition in the OCS radical cation
View Description Hide DescriptionSpectroscopy of the OCS^{+} ion in its ground and first excited states has been performed over a wide energy range using one‐photon dissociationspectroscopy. We used multiphoton ionization in the first step for state selective ion preparation in single well‐defined vibrational and spin–orbit states. This simplifies the ion spectra of the transition to the first excited A state considerably and thereover delivers the information of the ion ground state by using hot ion preparation. For the stretching vibrations anharmonicities have been observed and for the first overtone of the bending vibration Fermi resonances have been found. Rotational constants could be determined for the vibrational ground states of the X and A ionic states in both spin–orbit components. A new double resonance technique was applied to measure vibrational frequencies in the ionic Xground state.

Calculation of triatomic vibrational eigenstates: Product or contracted basis sets, Lanczos or conventional eigensolvers? What is the most efficient combination?
View Description Hide DescriptionNumerous practical methods have been described for exact quantum calculations of vibrational eigenstates (energy levels and wave functions) for three‐ and four‐atom molecules. Many descriptions are accompanied by bold claims of efficiency. Such claims are, unfortunately, difficult to test in the absence of fair comparisons on a single computer. The efficiency of these calculations depends above all (once the most appropriate coordinate system has been chosen) on clever choices of (i) the multidimensional basis set, and (ii) the Hamiltonian matrix eigensolver. In the first category come techniques such as the discrete variable representation (DVR) and basis contraction (also known as sequential adiabatic reduction or diagonalization truncation). In the second category, the Lanczos recursion is being increasingly applied. In a recent study taking the HCN/HNC molecule as a test case [R. A. Friesner, J. A. Bentley, M. Menou, and C. Leforestier, J. Chem. Phys. 99, 324 (1993)], reductions in computational effort of one to three orders of magnitude were found for a method combining basis contraction and Lanczos recursion, compared to one widely considered to be state of the art in which the Hamiltonian matrix is diagonalized conventionally [Z. Bačić and J. C. Light, J. Chem. Phys. 86, 3065 (1987)]. We have investigated this finding by developing a computer program which permits choosing both between direct product and two kinds of contracted basis (all derived from DVRs), and between Lanczos and conventional eigensolvers. It has been applied to the calculation of vibrational frequencies both of HCN/HCN up to 12 000 cm^{−1} and of H_{2}O up to 22 000 cm^{−1}, with a strict convergence criterion of 1 cm^{−1} in each case. We find the conclusions of Friesner et al. to be exaggerated: while a contracted/Lanczos method is consistently most efficient, other combinations, even the rather simple direct‐product Lanczos [M. J. Bramley and T. Carrington, J. Chem. Phys. 99, 8519 (1993)], are never as much as a factor of 5 more costly.

S _{1} excitation and zero kinetic energy spectra of partly deuterated 1:1 phenol–water complexes
View Description Hide DescriptionTwo‐photon, two‐color resonant‐enhanced multiphoton ionization (REMPI) spectra of the S _{1} state of isotopic 1:1 hydrogen‐bonded phenol–water clusters have been recorded. Up to three deuterium atoms are introduced in the phenolic OH group and/or the water molecule. The intermolecular vibrational structure found is in reasonable agreement with previously reported one‐color REMPI spectra, however, a partly different interpretation of the spectra is presented here. Zero kinetic energy photoelectron (ZEKE) spectra have been obtained via different intermediate S _{1} levels of the various isotopic complexes. The analysis of both the REMPI and the ZEKE spectra supports the new assignment of several vibrational bands observed in the REMPI spectra of the deuterated complexes where one or two hydrogen atoms are substituted by deuterium. For these deuterated complexes, the reassignment given here is based on the assumption that two different nonequivalent isomeric configurations are responsible for the structure observed in the REMPI spectra. This result is in clear contrast to the previously given interpretation where the spectra were analyzed in terms of only one isomer and the occurrence of Fermi resonances. Furthermore, accurate ionizationenergies are determined for all possible isomers of the various isotopic complexes and propensity rules for these values as a function of site‐specific deuteration have been found. In addition, the analysis of the intermolecular vibrational structure of the complex cations confirmed the assignment of the intermolecular stretch vibration.