Volume 83, Issue 4, 15 August 1985
Index of content:
83(1985); http://dx.doi.org/10.1063/1.449427View Description Hide Description
The fundamental band of CF+ in the X 1Σ+ state has been observed by infrared diode laser spectroscopy with magnetic field modulation of the dc discharge plasma. The CF+ ion was generated by a hollow cathode discharge in a mixture of CF4 and H2. From an analysis of the observed spectra, the following molecular constants were obtained: ν0=1766.3589(9), B e =1.720 366(81), α e =0.018 947(96), D e =6.179(17)×10− 6 in cm− 1 unit and r e =1.154 272(35) Å, with three standard errors in parentheses.
83(1985); http://dx.doi.org/10.1063/1.449428View Description Hide Description
Measurements of the temperature dependence of deuterium relaxation rates for the methylene groups of perdeuterated n‐nonadecane in a urea clathratesingle crystal are reported. Individual spectral densities J 1(ω0) and J 2(2ω0) were determined using Jeener–Broekaert experiments, and data obtained at two orientations of the main crystal axis were fit to a motional model which combines unrestricted rotational diffusion about the alkane long axis with restricted wobbling of the methylene group planes. Both motions are fast on the NMR time scale and both affect the observed, time averaged quadrupole coupling constant (e 2 q Q/h)eff=163 kHz. However, quadrupoletensor components appearing in the relaxation Hamiltonian should not be averaged over that part of the motion which is in fact responsible for the relaxation, and by fitting the relaxation data together with the observed quadrupolar splitting to the motional model described above we obtain a value ≥ 185 kHz for the methylene quadrupole coupling constant. This value of e 2 q Q/h has been averaged only over those vibrational motions which are too fast to contribute to observable relaxation.
Infrared‐microwave double resonance spectroscopy of the ν3 band of 1 1BF3 using a tunable diode laser83(1985); http://dx.doi.org/10.1063/1.449429View Description Hide Description
Pure rotational transitions in the ν3 state (E′) of 1 1BF3 due to vibrationally induced dipole moment are observed by infrared‐microwave double resonance using a tunable diode laser. The induced dipole moment is estimated to be 0.04+0.02 −0.01 D from the power broadening of the double resonance signals. The rotational constantC 0 is determined experimentally by use of the observed infrared and microwave transitions to be 5161.4(6) MHz.
83(1985); http://dx.doi.org/10.1063/1.449430View Description Hide Description
The infrared spectra of ND3⋅D2O and hydrogen or deuterium impurity in NH3⋅H2O or ND3⋅D2O at 100 K are reported for the first time. Their interpretation is aided by a D 2h pseudosymmetry caused by the heavy atoms being nearly coplanar in the P212121, D 4 2, crystal. No evidence of the possible disorder of the hydrogen atoms is observed. Oriented gas model calculations gave the approximate relative intensities of the unit cell components of the molecular vibrations. The site splitting and correlation splitting are comparable for ν3 and, probably, ν4 of ammonia; three unit cell components are observed instead of the six predicted under D 2, three components being calculated to have near‐zero intensity. The symmetric deformation of ammonia, ν2, yields two unit cell modes with significant intensity, separated by 37 cm− 1 for NH3 and 23 cm− 1 for ND3. The isotope frequency ratio for ν2 is lower than
for any other mode, so this large splitting must be due to intermolecular coupling, probably transition dipolar in origin. The two strong νOH (HDO) absorptions are 140 cm− 1 further apart than the two strong νOH (H2O) absorptions, a surprising result because intramolecular coupling is negligible because νO–H⋅⋅⋅N is ∼400 cm− 1 below νO–H⋅⋅⋅O. In contrast, νOD (D2O) yields four strong absorptions approximately centered with respect to the two strong νOD (HDO) absorptions. The O–D⋅⋅⋅N doublet is due to the B 1 and B 2 unit cell group components, the B 3 component being too weak to see, as is the case for ν2 of ammonia. The corresponding O–H⋅⋅⋅N doublet is unresolved. Use of the O–D⋅⋅⋅O–D’interaction force constant of the ice phases, −0.10 mdyn Å− 1, and oriented gas model calculations of the relative intensities shows that the O–D⋅⋅⋅O bands at 2390 and 2459 cm− 1 are due to the in‐phase (B 3) and out‐of‐phase (B 2) motions of the two O–D bonds in each chain of water molecules in each unit cell. In NH3⋅H2O the out‐of‐phase O–H⋅⋅⋅O vibration interacts, probably with 2ν4 of ammonia, and its intensity is dissipated among several weak features. We are unable to explain the difference between the coupled and uncoupled O–H⋅⋅⋅N frequencies, 2887 and 2825 cm− 1, in NH3⋅H2O. The bending mode of water is tentatively assigned at 1696, 1467, and 1243 cm− 1 for H2O, HOD, and D2O, respectively. The lattice absorptions are assigned to rotational or translational motion. The rotational modes of ammonia are assigned to the B 1, B 2, and B 3 unit cell modes that have significant intensity.
83(1985); http://dx.doi.org/10.1063/1.449431View Description Hide Description
A quantum mechanical approach based upon Floquet theory is used to study IR multiphoton excitation of the nonrotating OCS molecule within the frequency and power range of the cw CO2 laser. Using a classical field interacting with a quantum molecule in the dipole approximation, the effects of laser frequency and power are investigated by computing long‐time average transition probabilities, total energy absorption, and time‐dependent probabilities. While multiphoton excitation is found to occur at the most intense CO2 laser line [P(24)], high‐order excitation dominates near the weaker P(16) line, some 10 cm− 1 higher in photonenergy. Also, various types of time averaging and approximate dipole interactions are investigated.
83(1985); http://dx.doi.org/10.1063/1.449380View Description Hide Description
The transition probabilities for Hydrogen B 2pσ1Σ+ u (v′=32–35)←X 1Σ+ g (v″=0), C 2pπ1Π u (v′=11–13)←X (v″=0), and B′ 3pσ1Σ+ u (v′=5–8)←X (v″=0) were measured using synchrotron radiation in order to investigate the variation of the transition probabilities in the region of the dissociation threshold. The experimental data which agree with calculated probabilities indicate that B′ and C state continua may be of comparable intensities.
Molecular beam infrared spectra of dimers formed from acetylene, methyl acetylene, and ethene as a function of source pressure and concentration83(1985); http://dx.doi.org/10.1063/1.449381View Description Hide Description
Infrared spectra have been obtained for dimers formed from acetylene, methyl acetylene, and ethylene using a wide variety of free jet source conditions. An F‐center laser was used to excite various C–H stretch fundamentals in the range 3000–3300 cm− 1. Rotational structure was resolved in the spectra of both acetylene and methyl acetylene dimers when dilute mixtures of either gas in helium were expanded from high pressures. The spectrum of the ethylene dimer showed no such structure even when formed in very dilute mixtures. These results contradict previous suggestions that the vibrational relaxation lifetime is uniformly short for all polyatomic dimers.
Analysis of nuclear quadrupole interaction effects in electron spin‐echo modulation spectra by second‐order perturbation methods83(1985); http://dx.doi.org/10.1063/1.449382View Description Hide Description
The incorporation of nuclear quadrupoleinteraction into electron spin‐echo modulation spectra by second‐order perturbation methods has been developed for both two‐pulse and three‐pulse echo sequences. The results have been compared with exact numerical diagonalization of the Hamiltonian and with a first‐order perturbation treatment. Model calculations have been carried out for deuterium (I=1) and aluminum (I=5/2) nuclei. It is shown that the second‐order expressions can be used to obtain relatively accurate values for the number and distance of interacting nuclei at electron–nuclear distances greater than 0.26 nm. The procedure is more limited when the quadrupolar interaction exceeds the dipolar interaction when neither can be neglected.
83(1985); http://dx.doi.org/10.1063/1.449383View Description Hide Description
Electron paramagnetic resonance of Mn(II) ion doped in bis (ammonium) pentafluorostibnate is reported. Local charge compensation is proposed as the reason for the doubling of the expected single site. A ±20° rotation of the MnF3− 5 moeity about the crystallographic a axis has been attributed to charge compensation processes. The Dtensor is found to have the values D z z =0.0358 cm− 1, D y y =−0.028 62 cm− 1, D x x =−0.007 26 cm− 1; the Mn hyperfine coupling is found to be −0.0095 cm− 1. The apical flourine does not give resolved hyperfine coupling, while the four basal flourine atoms give hyperfine couplings in the range a max=0.0018 cm− 1, a min=0.0015 cm− 1.
Host‐lattice systematics of EPR spectra of Mn2 +‐doped isomorphic metal hexakisantipyrine perchlorate and EPR of Cu2 + in copper pentakisantipyrine perchlorate83(1985); http://dx.doi.org/10.1063/1.449384View Description Hide Description
X‐band EPR measurements on Mn2 +‐doped single crystals of isomorphous metal hexakisantipyrine perchlorate (metal=Ca, Cd, Mg, Co, and Pb) have been performed. For the case of calcium and cadmiummetal hosts, the measurements were made from room temperature down to liquid helium temperature, while for the remaining metal hosts the measurements were made only at room temperature. The spin Hamiltonian parameters are rigorously evaluated using a least‐squares fitting computer technique, especially adapted to electron‐nuclear spin coupled systems. As for the systematics of the spin Hamiltonian parameters, at room temperature the variation of the zero field splitting parameters b 0 2 and b 0 4 is found to be approximately linear in the host metal ion radius. In order to estimate the Cu2 +–Mn2 + exchange interaction, 5%–50% of Ca2 + ions in Mn2 +‐doped calcium hexakisantipyrine perchlorate were substituted for by Cu2 +, and the EPR spectra were recorded from room temperature down to liquid helium temperature. However, even at liquid helium temperature, the presence of the paramagnetic ion Cu2 + in this host caused no significant change of the g value for Mn2 + as compared with that in the pure diamagnetic host indicating negligible Cu2 +–Mn2 + exhange constant. EPR measurements on Cu2 + in copper pentakisantipyrine perchlorate were also made at room, liquid nitrogen, and liquid helium temperatures and the principal values and direction cosines of the principal axes of the g and A tensors were estimated, using a rigorous least‐squares fitting procedure.
83(1985); http://dx.doi.org/10.1063/1.449385View Description Hide Description
Vibration‐rotation absorption lines of HCS+ have been detected between 718 and 816 cm− 1 by diode laser spectroscopy, and assigned to P‐, Q‐, and R‐branch components of the ν2 bending fundamental. Their accurate analysis yields the first measurements of the rotational parameters B and D and the l‐doubling constant q for the 0110 level. The band center was determined to be 766.453 (1) cm− 1.
Vibrational relaxation in liquid hydrogen and deuterium bromide—The influence of self and distinct correlation functions on the isotropic and anisotropic Raman line shape83(1985); http://dx.doi.org/10.1063/1.449386View Description Hide Description
Both, the isotropic and anisotropic Raman line shapes of orthobaric liquid hydrogen and deuterium bromide are measured at 295 K and close to the triple point (185 K). Concentration dependent studies in HBr/DBr mixtures allow an experimental separation of the resonant transfer mechanism from other line broadening mechanisms. It is found that the anisotropic spectra are nearly unaffected by isotopic dilution, whereas the isotropic ones show a blue shift and a narrowing with increasing isotopic dilution. The overall contribution of the transfer mechansim to the line broadening becomes most pronounced at the lower temperature. The results are discussed in terms of a recent Raman line shape theory of Bratos and Tarjus.
Analysis of torsional spectra of molecules with two internal C 3v rotors. XXIII. Microwave, infrared, and Raman spectra, barriers to internal rotation, and vibrational assignment of 3,3,3‐trifluoro‐2‐methylpropene83(1985); http://dx.doi.org/10.1063/1.449387View Description Hide Description
The microwave spectrum of 3,3,3‐trifluoro‐2‐methylpropene, H2C=C(CH3)CF3 has been recorded from 18.5 to 39.0 GHz. Only a‐type transitions were observed and R‐branch assignments have been made for the ground vibrational state as well as for three vibrational excited states of the CF3 torsion and one excited state of the CH3 torsion. The rotational constants for the ground vibrational state were found to have the following values: A=3549.25±0.35, B=2465.82±0.05, and C=1978.25±0.02 MHz. The dipole moment components were determined from the Stark effect to be ‖μ a ‖=2.44±0.01, ‖μ b ‖=0.59±0.09, and ‖μ t ‖=2.51±0.03 D. From an analysis of the internal rotational splittings, the threefold barrier for the methyl group was found to be 603±19 cm− 1 (1.72 kcal/mol). This value is consistent with the value of 610±4 cm− 1 (1.74 kcal/mol) obtained from the far infrared spectrum where the fundamental was assigned at 160.9 cm− 1, but only if kinetic coupling between the perfluoromethyl and methyl torsion is taken into account. The CF3 torsional mode was observed at 55.9 cm− 1 from which a threefold periodic barrier of 743±7 cm− 1 (2.12 kcal/mol) was calculated. No appreciable potential coupling was found between the two C 3v rotors. The infrared (3500 to 30 cm− 1) and Raman spectra (3500 to 10 cm− 1) have been recorded for both the gas and solid states. Additionally, the Raman spectrum of the liquid was recorded and qualitative depolarization values were obtained. All of the normal modes have been assigned based on band contours, depolarization values, and group frequencies. These results are compared to the corresponding quantities in some similar molecules.
Spectra and structure of organophosphorus compounds. XXIV. Microwave, infrared, and Raman spectra, conformational stability, and vibrational assignment for chloromethylphosphonic difluoride83(1985); http://dx.doi.org/10.1063/1.449388View Description Hide Description
The microwave spectrum of chloromethylphosphonic difluoride, ClCH2P(O)F2, has been investigated in the region from 26.5 to 39 GHz. The a‐type R branch transitions have been assigned for both the 3 5Cl and 3 7Cl isotopic species for the t r a n s conformer on the basis of the rigid rotor model. For the ground vibrational state the rotational constants for the 3 5Cl isotope were found to be A = 4392.4±2.3, B=1543.36±0.01, and C=1512.30±0.01 MHz and for the 3 7Cl isotope:A=4395.3±2.7, B=1502.04±0.01, and C=1472.54±0.01 MHz. With reasonably assumed structural parameters for the C–H and P=0 distances as well as the HCH angle, a diagnostic least‐squares adjustment was utilized to obtain the other six structural parameters. The dipole moment components were determined from the Stark effect to be ‖μ a ‖ =2.28±0.05, ‖μ b ‖ =0.75±0.02, and ‖μ t ‖ =2.40±0.02 D. The infrared (3500–40 cm− 1) and Raman (3500–20 cm− 1) spectra of the gas and solid have been recorded. Additionally, the Raman spectrum of the liquid has been recorded and qualitative polarization values have been obtained. Both
the t r a n s and g a u c h e conformers have been identified in the vibrational spectrum of the fluid phases. From a temperature study of the Raman spectrum of the liquid phase the enthalpy differencebetween the t r a n s and g a u c h e conformers was determined to be 370±50 cm− 1 (1.06 kcal/mol) with the t r a n s conformer being thermodynamically preferred. Band contour simulation of the infrared gas phase bands also shows that the t r a n s conformer is more stable in this phase. Upon crystallization only the t r a n s conformer remains in the solid state. The asymmetric torsion for the t r a n s conformer was observed as a series of closely spaced Q branches beginning at 82.5 cm− 1 and falling to lower frequency and the corresponding transitions for the g a u c h e conformer begin at 72.9 cm− 1. These transitions have been used to obtain the potential constants for the asymmetric rotation. All of the normal modes have been assigned based on band contours, depolarization values, and group frequencies. A normal coordinate calculation has been carried out by utilizing a modified valence force field to calculate the frequencies and the potential energy distribution. All of these results are compared to similar quantities in some corresponding molecules.
83(1985); http://dx.doi.org/10.1063/1.449389View Description Hide Description
We have determined what orientation and size information can be obtained for colloidaldispersions of Rayleigh particles from light scatteringmeasurements. For noninteracting particles and single scattering, a maximum of 15 moments of the orientation/size distribution can be obtained by using a minimum of (i) three distinct orientations of linearly polarized incident light; (ii) three scattering angles θ in one scattering plane; and (iii) three different polarization orientations of the detector. The information obtainable from less complete experiments has also been determined. Specifically, only six combinations of the above fifteen moments can be determined if unpolarized incident light is used. For polydisperse systems with random orientation, two moments of the size distribution can be determined. For polydisperse particles of the same orientation, (i) the orientation and three moments can be determined for axisymmetric particles and (ii) the orientation and six moments can be determined for nonaxisymmetric particles. The results provide guidance for design of instrumentation and experiments.
The experimental and theoretical expressions for the molecular electronic oscillator strength in solution83(1985); http://dx.doi.org/10.1063/1.449390View Description Hide Description
In this paper we propose the appropriate fundamental definition of the oscillator strength in solution and clearly show that both the experimental and theoretical expressions of the oscillator strength should contain refractive index correction factors of α and β, respectively. Therefore, in the discussion of the solvent effects on the oscillator strength the experimental and theoretical expressions containing the correction factors should be used instead of the usual expressions of α=1 and β=1.
Direct determination of single‐crystal parameters for axial paramagnetic resonance centers in polycrystalline‐amorphous substances83(1985); http://dx.doi.org/10.1063/1.449391View Description Hide Description
The paramagnetic resonance powder spectrum of an electron or nuclear spin system involving an isotropic Zeeman and an axially symmetric, first‐order fine‐structure splitting has been numerically investigated for the purpose of finding a simple, direct, and accurate method for determining its single‐crystal parameters in polycrystalline‐amorphous samples. It is shown that from the positions and relative intensities of some selected first‐ and second‐derivative peaks of the axial fine‐structure powder spectrum, one can directly determine with high accuracy the associated coupling constant, single‐crystal line shape, and single‐crystal linewidth for the external magnetic field perpendicular as well as parallel to the axially symmetric axis. The results of an experimental application of this method to the case of a randomly oriented zinc chelate biradical system are presented. The new powderspectrum method is applicable to first‐order axially symmetric ESR and NMR quadrupole and dipole‐dipole pair centers with isotropic g values under rigid state or slow tumbling orientational motion in polycrystalline‐amorphous substances.
Theoretical study of the spin‐orbit autoionization in molecules application to the HI photoionization spectrum83(1985); http://dx.doi.org/10.1063/1.449392View Description Hide Description
A theoretical study of the spin‐orbit autoionization in molecules with 2Π state ion cores is presented. The multichannel quantum defect theory is used with an a b i n i t i o calculation of the relevant electronic quantities. In the application to the HI photoionizationspectrum the energy positions of the observed resonances between the 2Π1/2 and 2Π3/2ionization thresholds are well reproduced. The importance of the l mixing especially for the π3σ channels is stressed. An attempt to include the S‐uncoupling part of the rotational operator in the calculations gives rise to additional autoionization peaks, associated with a new type of rotational autoionization specific to 2Π‐state cores. Theoretical predictions are also made for the angular distribution and spin polarization parameters of the photoelectron in the 1155–1168 Å energy range.
Transmission function vs energy splitting in tunneling calculations. II. Computer simulation results83(1985); http://dx.doi.org/10.1063/1.449393View Description Hide Description
An idealized model for the quantum tunneling of a particle in interaction with a heat bath is studied by computer simulation. The model may be motivated by consideration of a bound hydrogen–oxygen pair in a metal lattice; the H atom is treated quantum mechanically, the O atom is treated classically, and a double‐well potential couples the two. In order to represent the O atom interactions with the rest of the lattice as heat bath, its motion is described by a classical Langevin equation.Computer simulation of the model shows that, with all other parameters held fixed, tunneling through low energy barriers is governed by energy splitting, while for high energy barriers the transmission approach agrees well with simulation results.
83(1985); http://dx.doi.org/10.1063/1.449394View Description Hide Description
We report state‐to‐state integral inelastic cross sections for rotational energy transfer in rigid rotor HF–Li collisions, at a relative translational energy of 8.7 kcal mol− 1. The results have been analyzed in terms of power gap law, information theoretic synthesis using energy and angular momentum constraints, and energy corrected sudden and energy corrected sudden‐power law scaling relations.