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Volume 103, Issue 1, 01 July 1995

Partially coherent anti‐Stokes Raman scattering (PCARS): A comparative band‐shape analysis of the spontaneous Raman and PCARS spectra of toluene
View Description Hide DescriptionPartially coherent anti‐Stokes Raman scattering (PCARS) spectrum of liquid toluene has been measured. The observed shape of the 1004 cm^{−1} band is asymmetric unlike that of the spontaneous Raman spectrum. A least‐squares fitting shows that this asymmetric PCARS band‐shape is fitted well to ‖χ^{(3)}‖^{2} but not to the imaginary part of χ^{(3)}. The origin of the observed band asymmetry is the nonresonant term of χ^{(3)}, which is real and does not affect the spontaneous Raman band shapes. These results support our previous interpretation that the PCARS intensity originates from the relaxation of the CARS phase matching condition due to the optical inhomogeneity of the sample.

Absolute integrated cross sections for some O_{2} Herzberg I transitions near 248–249 nm
View Description Hide DescriptionA frequency doubled tunable dye laser system with ∼0.4 cm^{−1} resolution was used to measure the integrated absorption cross sections of more than 20 rotational transitions in the O_{2} Herzberg I (A ^{3}Σ^{+} _{ u }←X ^{3}Σ^{−} _{ g }) 8‐0 and 9‐0 vibrational bands near 248 nm and 249 nm. Oxygen pressures from 200 to 800 Torr and path lengths from 5 to 25 m were employed. The measured absorbances were fitted using a nonlinear least squares analysis and Beer’s Law to obtain absolute values for the individual transition integrated cross sections in good agreement with a recent spectral simulation and experimental data. By using the spectral simulation in conjunction with the present experimental results, total oscillator strengths in reasonable agreement with literature values were estimated for the 8‐0 and 9‐0 vibrational bands.

Study of the overtone C–O stretching band of methanol by multiple resonance spectroscopy
View Description Hide DescriptionTwo microwave‐sideband CO_{2} lasers have been used with a molecular‐beam electric‐resonance spectrometer to study the overtone C–O stretching vibration of methanol. Infrared‐infrared double‐resonance results have been obtained for levels involving the K=1 and 2, A symmetry, and the K=2, E _{2} symmetry species. In the A torsional symmetry case, radio frequency‐infrared multiple resonance was used to obtain accurate asymmetry splittings for the v _{co}=1 and 2, C–O stretching states. The asymmetry splitting constants determined for these states are in good agreement with the literature values for the first excited C–O stretching states. However, the nearly factor‐of‐2 change in the K=2 asymmetry splitting constant for the v _{co}=2 level compared to the v _{co}=0 and 1 level results suggests that this state is weakly perturbed. The overtone transition frequencies obtained in this work were combined with previous overtone Fourier‐transform results in a global fit to a torsion–rotation Hamiltonian to refine the fundamental molecular constants for the second‐excited C–O stretching state. The v _{co}=2 torsional barrier height is found to be 372.227(3) or 374.984(7) cm^{−1} depending on data set used. In the analysis the overtone vibrational energy origin is constrained to 2054.831 13 cm^{−1}. This barrier can be compared to the v _{0}=0 and 1 values of 373.5421 and 392.35 cm^{−1}, respectively.

Ab initio study of styrene and β‐methyl styrene in the ground and in the two lowest excited singlet states
View Description Hide DescriptionThe structure and vibrational frequencies of styrene and trans‐β‐methyl styrene in the lowest three singlet states (S _{0}, S _{1}, and S _{2}) have been calculated using ab initio quantum chemical methods. The frequencies are compared with experimental data obtained in the bulk and in a supersonic jet. The calculation shows that in the ground state the molecules have a broad shallow potential as a function of the torsional angle, are essentially planar, but may be slightly bent. In the S _{1} and S _{2} states, the molecules are planar; In S _{1}, the main structural change is in the aromatic ring, that is somewhat expanded. In S _{2}, the C=C vinyl double bond elongates, while the C1—Cα single bond becomes shorter, bringing these two bonds to almost equal length. Correlation diagrams connecting ground state vibrational modes with ones belonging to electronically excited states are given; they show that for many out‐of‐plane modes the vibrational frequencies decrease upon electronic excitation. This is accounted for in terms of the changes in the π electron distribution taking place upon optical excitation that result in decreasing the force constants characterizing these vibrations. The frequencies of most in‐plane modes change very little, but mixing between S _{0} modes is indicated in some cases, and a few vibrations, among them a Kekulé‐type mode, undergo considerable change. The relation to the spectroscopy of the corresponding transitions in benzene is briefly discussed.

S _{0}↔S _{1} transition of trans‐β‐methyl styrene: Vibronic structure and dynamics
View Description Hide DescriptionThe fluorescence excitation and emission spectra of trans‐β‐methyl styrene have been measured in a supersonic jet. A complete vibrational assignment of the S _{0} and S _{1} states’ frequencies is reported, assisted by ab initio quantum chemical calculations and by comparison with the IR spectrum. The fluorescence lifetime, τ_{ f }, of the isolated molecule changes monotonously from 24.5 to 15 ns as the excitation energy increases from the origin band to an excess of 3000 cm^{−1}. The fluorescence quantum yield from the zero‐point energy level of S _{1} is about 38%, similar to the liquid solution value; The major radiationless process being intersystem crossing to a triplet level. The increasing congestion of the emission spectra as the excitation energy is increased is interpreted as due to intramolecular vibrational energy redistribution. The data are consistent with the fact that in the isolated molecule intramolecular vibrational energy redistribution is faster than intersystem crossing. Beyond an excess energy of about 3200 cm^{−1}, a more pronounced decrease in τ_{ f } is observed, indicating that the barrier to trans–cisisomerization on the S _{1} surface, in the isolated molecule is higher than 3200 cm^{−1}.

Electronic absorption spectra of linear carbon chains in neon matrices. I. C^{−} _{6}, C_{6}, and C_{6}H
View Description Hide DescriptionElectronic absorption spectra of linear C^{−} _{6}, C_{6}, and C_{6}H have been identified in neon matrices at 5 K. The species were produced by codepositing mass selected cations and anions with neon. The ions were generated in a hot cathode discharge source using diacetylene. The spectra of C^{−} _{6} and C_{6} could also be observed using a pure carbon anion source or laser vaporization of graphite. The assignment is based on the mass selection, experimental and spectroscopic evidence, leading to the location of the 0^{0} _{0} transitions of C^{−} _{6}: ^{2}Π_{ g }←X ^{2}Π_{ u }, C_{6}: ^{3}Σ^{−} _{ u }←X ^{3}Σ^{−} _{ g }, and C_{6}H: ^{2}Π←X ^{2}Π at 16 458, 19 558, and 18 854 cm^{−1}, respectively. The frequencies of the symmetric carbon stretching vibrations have been obtained for these species in their excited electronic states.

Electronic absorption spectra of linear carbon chains in neon matrices. II. C^{−} _{2n }, C_{2n }, and C_{2n }H
View Description Hide DescriptionAbsorption spectra observed between 400 and 2500 nm in 5 K neon matrices have been assigned to electronic transitions of linear C^{−} _{2n } (n=2–10): ^{2}Π←X ^{2}Π, C_{2n } (n=3–7): ^{3}Σ^{−} _{ u }←X ^{3}Σ^{−} _{ g }, and C_{2n }H (n=3–8): ^{2}Π←X ^{2}Π chains. The species have been produced by mass selected deposition of cations or anions produced in a hot cathode discharge source (C_{2n }, C^{−} _{2n }, C_{2n }H) and by laser vaporization of graphite (C_{2n }, C^{−} _{2n }). In addition to experimental and chemical evidence, the dependence of the absorption wavelength on the number of carbon atoms was used to assign the electronic transitions. Infrared absorptions which were recorded around 2000 cm^{−1} are attributed to asymmetric stretching frequencies of C_{8}, C_{10}, and C_{12}. This is based on correlation of their intensities with the identified electronic bands. The possible relevance of the electronic spectra of these carbon chains to astrophysical observations of diffuse interstellar bands is discussed.

Coupled channel bound states calculations for alkali dimers using the Fourier grid method
View Description Hide DescriptionThe Fourier grid Hamiltonian method is shown to be a powerful method to provide an accurate determination of the bound state spectra of coupled electronic states in alkali dimers. Using accurate ab initio potentials, the perturbations in the spectra of the coupled states A ^{1}Σ^{+} _{ u } and b ^{3}Π_{ u } in Na_{2} are reproduced in excellent agreement with spectroscopic studies. A few predictions are also presented for the heavier species Cs_{2}, for which a complete study, both experimental and theoretical, is still needed.

Laser‐induced fluorescence studies of jet‐cooled S_{2}O: Axis‐switching and predissociation effects
View Description Hide DescriptionLaser‐induced fluorescence spectroscopy has been used to probe the intense C̃ ^{1} A′–X̃ ^{1} A′ (π*←π) electronic system of S_{2}O (315–340 nm) under supersonic free‐jet conditions that yield effective rotational temperatures of roughly 1 K. Least‐squares analysis of high‐resolution scans performed on the 2^{ v } _{0}(v=0–5) progression, where ν_{2} corresponds to the S–S stretching mode, not only furnish refined band origins and rotational constants, but also provide evidence for an axis‐switching effect in this asymmetric triatomic species. Based on the limited set of vibronic bands examined in the present study, the harmonic frequency and anharmonicity for S–S stretching motion in the C̃ state are determined to be ω_{2}=415.2(4) cm^{−1} and x _{22}=−2.10(6) cm^{−1}, respectively. Predissociation of the C̃ ^{1} A′ potential energy surface is found to become more pronounced with increasing excitation of the ν_{2} mode. Collision‐free lifetime data, obtained either directly from time‐resolved fluorescence decay profiles or indirectly from measurements of broadened spectral linewidths, permit formulation of a simple, one‐dimensional tunnelingmodel which predicts the excited state predissociation barrier to be located in the vicinity of the 2^{6} vibrational level. These results, as well as possible candidates for the electronic manifold responsible for the predissociation process, are discussed in light of preliminary ab initio calculations.

Electronic and vibrational excitation of acrylonitrile by low and intermediate energy electrons
View Description Hide DescriptionElectronic and vibrational excitation of acrylonitrile induced by 3–50 eV energyelectrons has been investigated by the electron energy loss spectroscopy. Electronic excitation spectra have been recorded for 30 and 50 eV impact energies at a 10° scattering angle in the energy loss range from 5.5 to 11.5 eV, corresponding to the excitation of electrons belonging to the outermost‐valence‐shell molecular orbitals. We have reviewed the assignment of the valence excited states occurring in the 5.5–9 eV energy loss region. The vibrational patterns associated with the two lowest‐energy singlet valence excited states have also been re‐examined. Moreover, we have proceeded for the first time to the analysis and attribution of several Rydberg series converging to the ionic ground state and to its two lowest‐energy electronic excited states. The study of the excitation function of the C—H stretching modes of acrylonitrile in the 3–11 eV electron impact energy range has shown evidence of a broad shape resonance built on the electronic ground state of the molecule and centered at 5.85 eV. This resonance contributes to a preferential excitation of the C—H stretching modes suggesting that the charge distribution of the additional electron is very likely that of a σ*(C—H) valence molecular orbital. A comparison has been made between the resonances observed in C_{2}H_{4} and CH_{2}CHCN, in order to discuss the symmetry of the resonant state and also to analyze the substitution effect of the cyanogen group.

Pure rotational spectrum of FeCO
View Description Hide DescriptionThe rotational spectrum of the FeCO radical has been observed by using a Fabry–Perot type Fourier‐transform microwave spectrometer combined with a pulsed discharge nozzle. The radicals have been generated by a discharge of Fe(CO)_{5} diluted in Ar, and subsequently cooled down to a few kelvins in a supersonic free jet. Four spectral lines observed in the 8.5–35.5 GHz region have been assigned to the transitions in the Ω=0 spin component of ^{56}FeCO, the most abundant isotopic species, in the ^{3}Σ^{−} electronic ground state, and analyzed to obtain the spectroscopic constants. Transitions in the Ω=±1 spin components have not been detected due to the small population in these levels. Spectra of other four isotopic species, ^{54}FeCO, ^{57}FeCO, Fe^{13}CO, and Fe^{13}C^{18}O, have also been observed to confirm the identification of the species, yielding the substituted coordinates of the molecule. The determined Fe–C bond length [r _{ s }(Fe–C)=1.727 Å] is about 0.1 Å shorter than that of Fe(CO)_{5}, but the C–O bond length [r _{ s }(C–O)=1.160 Å] is almost the same as that of Fe(CO)_{5}, which indicates stronger Fe–CO bonding than that of Fe(CO)_{5}. We have searched for the 34 GHz transition of the radical toward several molecular clouds on various evolutionary stages by using the Nobeyama 45 m radio telescope. The signal of this radical was not detected with rms noise level of 10 mK, which gives an upper limit for the molecular column density of (2–4)×10^{12} cm^{−2}.

Direct simulation of slow‐motion electron spin resonance spectra by solving the stochastic Liouville equation in the time domain with stochastic dynamics in the form of trajectories
View Description Hide DescriptionA new method to solve the stochastic Liouville equation in the time domain has been developed. The effective and accurate algorithm designed conserve the norm of the propagator at every time step. The algorithm is not dependent on how the fluctuations are generated. The method is applied to solve the stochastic Liouville equation of an electron spin, S=1/2, coupled to a nuclear spin system with spin quantum number I=1. The calculated slow‐motion electron spin resonance(ESR) line shapes presented are for a model where the stochastic time dependent spin‐lattice coupling was obtained from a Brownian dynamic simulation of restricted reorientation in a cone potential. These spectra were then compared with the spectra obtained by solving the stochastic Liouville equation (SLE) using the eigenfunction expansion method. All spectra conform exactly and the computer power used by the two methods are similar.

Predissociation mechanism and spin‐rotation constant of the HCO B̃ ^{2} A′ state
View Description Hide DescriptionFormyl radicals produced from photolysis of acetaldehyde at 310 nm were supersonically cooled and detected via the B̃–X̃ transition using the laser‐induced fluorescence(LIF) technique. Spectra at 0.16 cm^{−1} resolution and fluorescence lifetimes of HCO B̃(0,0,0), (0,0,1), and (0,1,0) levels were measured. The observed lifetimes decrease rapidly with variation of the rotational quantum number K _{ a } from 0 to 2 but slowly with the rotational quantum number N from 0 to 8. Experimental data indicate that the B̃ state is coupled to a predissociating state via an a‐type Coriolis interaction to account for the rotationally dependent lifetime for the low vibrational levels of the HCO B̃ state. Correction of the fluorescence quantum yield for individual rotational states is necessary to obtain accurate ground state populations by LIF when using the B̃–X̃ transitions. The intensity distribution of the two spin states observed implies a negative value of the spin‐rotation parameter for the B̃ state, in contrast with the ground electronic state.

Cavity ringdown laser absorption spectroscopy and time‐of‐flight mass spectroscopy of jet‐cooled silver silicides
View Description Hide DescriptionThe cavity ringdown technique has been employed for the first spectroscopic characterization of the AgSi molecule, which is generated in a pulsed laservaporization plasma reactor. A total of 20 rovibronic bands between 365 and 385 nm have been measured and analyzed to yield molecular properties for the X, B, and C ^{2}Σ states of AgSi. A time‐of‐flight mass spectrometer simultaneously monitors species produced in the molecular beam and has provided the first direct evidence for the existence of polyatomic silver silicides. Comparison of the AgSi data to our recent results for the CuSi diatom reveals very similar chemical bonding in the two coinage metal silicides, apparently dominated by covalent interactions.

Perturbation treatment of pump–probe laser–molecule interactions: An application to the fluorescence from the S _{1} state of α‐NPO
View Description Hide DescriptionTime‐dependent perturbation theory, together with a (minimal) molecular model consisting of three energy levels (S _{0},S _{1},S _{3}), is used to investigate the spectroscopy and the dynamics of fast time resolved, two‐photon, two‐color, pump–probe experiments, involving the direct S _{0}→S _{1} two‐photon excitation of α‐NPO. In particular the theory is used to examine the Θ‐dependence of the fluorescence signal from the S _{1} state, where Θ is the angle between the polarization vectors of the pump and probe lasers, for fixed (zero) time delay between the laser pulses. It is predicted, in contradistinction to the cos^{2} Θ dependence of the fluorescence signal from the S _{2} state of azulene arising from the sequential two‐photon S _{0}→S _{1}→S _{2} transition, that the signal from the S _{1} state of α‐NPO can vary between pure cos^{2} Θ and pure cos^{4} Θ dependencies and that secondary maxima in the signal, as a function of Θ, can occur for certain laser intensities. Also reported is a new series of experiments for α‐NPO, motivated by the theory, that yields results for the fluorescence intensity of the S _{1} state, as a function of Θ and laser intensity, in agreement with the theoretical predictions. Comparison of experiment and theory is used to estimate the relative orientations of the relevant transition and permanent dipole moments, and the transition moment between the S1 and S _{3} states of α‐NPO. The important role played by the permanent dipoles of the S _{0} and S _{1} states, and the importance of including averages over the relative laser phase, the jitter in the time‐delay, and the orientations of the absorbing molecules, is emphasized in the theoretical analysis of the problem.

Coherence transfer in three‐level systems: Controlled violation of adiabaticity and antiparallel double resonant irradiation
View Description Hide DescriptionIt is shown by theory and experiment how coherent superpositions of quantum states in three‐level systems can be manipulated by irradiating two connected transitions with two resonant fields with suitably shaped time‐dependent amplitudes and phases. Three variants are discussed in detail; (i) adiabatic coherence transfer (ACT) between two transitions, which may be either allowed or forbidden; (ii) nonadiabatic transfer of coherence to a nonirradiated transition by controlled violation of adiabaticity (CVA); (iii) coherence transfer to a nonirradiated transition by antiparallel double resonant irradiation (APDRI). A geometrical representation of these experiments gives a clear physical picture of the phenomena and provides a tool for the development of new methods. The principles are illustrated experimentally by applications to magnetic resonance of deuterium (I=1) in anisotropic phase at high magnetic field, but could also be applied to three level‐systems in nuclear quadrupole resonance, optics, and other areas of spectroscopy.

Guided‐ion beam measurements of the O^{+}(^{4} S)+Xe charge‐transfer reaction
View Description Hide DescriptionGuided‐ion beam integral cross section measurements, product ion time‐of‐flight (TOF) measurements, and doubly differential cross sections are presented for the O^{+}(^{4} S)+Xe→O+Xe^{+}charge‐transferreaction. The integral cross section is observed to increase monotonically with mean center‐of‐mass collision energy (E _{ T }) from 0.72 Å^{2} at 0.1 eV to 26.9 Å^{2} at 35.2 eV. Product ion TOF measurements show that the primary contribution to the charge‐transfer cross section arises from a direct electron transfer at long range of the Demkov type. The collision energy dependence of the cross section for center‐of‐mass (c.m.) forward‐scattered Xe^{+} ions reveals that this minor contribution to the total cross section arises from a hard‐sphere‐type scattering that primarily involves a Landau–Zener‐type diabatic curve crossing at shorter range. Doubly differential cross sections at 4.4 eV indicate that translational to product internal energy transfer is inefficient even at small impact parameters and that the spin‐allowed Xe^{+}(^{2} P)+O(^{3} P) product channels are preferentially populated.

Ab initio molecular dynamics simulation of the solvation and transport of hydronium and hydroxyl ions in water
View Description Hide DescriptionCharge defects in water created by excess or missing protons appear in the form of solvated hydronium H_{3}O^{+} and hydroxyl OH^{−}ions. Using the method of ab initiomolecular dynamics, we have investigated the structure and proton transferdynamics of the solvation complexes, which embed the ions in the network of hydrogen bonds in the liquid. In our ab initiomolecular dynamics approach, the interatomic forces are calculated each time step from the instantaneous electronic structure using density functional methods. All hydrogen atoms, including the excess proton, are treated as classical particles with the mass of a deuterium atom. For the H_{3}O^{+} ion we find a dynamic solvation complex, which continuously fluctuates between a (H_{5}O_{2})^{+} and a (H_{9}O_{4})^{+} structure as a result of proton transfer. The OH^{−} has a predominantly planar fourfold coordination forming a (H_{9}O_{5})^{−} complex. Occasionally this complex is transformed in a more open tetrahedral (H_{7}O_{4})^{−} structure. Proton transfer is observed only for the more waterlike (H_{7}O_{4})^{−} complex. Transport of the charge defects is a concerted dynamical process coupling proton transfer along hydrogen bonds and reorganization of the local environment. The simulation results strongly support the structural diffusion mechanism for charge transport. In this model, the entire structure—and not the constituent particles—of the charged complex migrates through the hydrogen bond network. For H_{3}O^{+}, we propose that transport of the excess proton is driven by coordination fluctuations in the first solvation shell (i.e., second solvation shell dynamics). The rate‐limiting step for OH^{−}diffusion is the formation of the (H_{7}O_{4})^{−} structure, which is the solvation state showing proton transfer activity.

An explanation of the highly efficient magnetic quenching of fluorescence in intermediate case molecules based on two manifold models
View Description Hide DescriptionThe magnetic quenching of fluorescence in intermediate case molecules is modeled by including two triplet manifolds {‖b _{ j }〉} and {‖c _{ j }〉} mutually shifted by the zero‐field splitting E _{gap} (though a triplet has three spin sublevels); the {‖b _{ j }〉} are coupled to a bright singlet state ‖s〉 by intramolecular interactionV and the two manifolds are coupled by a magnetic field. For the two manifold Bixon–Jortner model where the level spacings and the couplings to ‖s〉 are constant and no spin–vibration interactions exist (the Zeemaninteraction connects only the spin sublevels of the same rovibronic level j), there are two sets of field dressed eigenstates, {‖b̂_{ j }〉} and {‖ĉ_{ j }〉}, of the background Hamiltonian H−V. ‖b̂_{ j }〉 and ‖ĉ_{ j }〉 are liner combinations of ‖b _{ j }〉 and ‖c _{ j }〉. We call the energy structure ‘‘eclipsed (E)’’ when the two sets of dressed states overlap in energy and call it ‘‘staggered (S)’’ when every ‖b̂〉 state is just between two adjacent ‖ĉ〉 states.
The E and S structures alternatively appear with increasing Zeeman energy h _{ Z }. As h _{ Z } increases, the number of effectively coupled background levels, N _{eff}, increases for the S structure but remains unchanged for the E structure. The S structure is in accord with the experimental result that the quantum yield is reduced to 1/3 at anomalously low fields (h _{ z }/E _{gap}≪1): in the far wing regions of the absorption band the mixing between the manifolds is determined by the ratio h _{ Z }/E _{gap}, but near the band center the intermanifold mixing is enhanced by the presence of ‖s〉. Using a random matrix approach where H is constructed of the rotation–vibration Hamiltonians H _{ B } and H _{ C } arising from the manifolds {‖b _{ j }〉} and {‖c _{ j }〉}, we show that an S structure can be formed in real molecules by nonzero ΔH _{ BC }≡H _{ B }−H _{ C }−E _{gap} (E _{gap} is the zero‐field splitting at the equilibrium nuclear configuration). Indirect spin–vibration interactions lead to ΔH _{ BC }≠0; the vibrational ΔH _{ BC } caused by spin–spin and vibronic interactions and the rotational ΔH _{ BC } caused by spin–rotation and rotation–vibration interactions. The matrix elements of H are written down in terms of the eigenfunctions {‖j〉} of the average Hamiltonian (H _{ B }+H _{ C })/2. If the vibrational modes are strongly coupled (the energies of levels are given by a Wigner distribution and the coupling strengths are given by a Gaussian distribution), the vibrational 〈j‖ΔH _{ BC }‖j′〉 for wave functions of roughly the same energy are Gaussian random.
As the rms of 〈j‖ΔH _{ BC }‖j′〉 approaches the average level spacing (on excitation into higher vibrational levels), the efficiency of magnetic quenching becomes as high as in the S case. Nonzero 〈j‖ΔH _{ BC }‖j′〉 let isoenergetic levels belonging to different manifolds vibrationally overlap: the ΔH _{ BC }, together with the magnetic field, causes level repulsion leading to the S structure and opens up isoenergetic paths between the manifolds. The efficient magnetic quenching in pyrazine can be explained by the vibrational ΔH _{ BC }, since the S _{1}–T _{1} separation is as large as 4500 cm^{−1}. If Coriolis couplings cause K scrambling considerably, the rotational ΔH _{ BC } mixes {‖j〉}. This mechanism explains the rotational dependence of magnetic quenching in s‐triazine of which S _{1}–T _{1} separation is only ∼1000 cm^{−1}.

Analytical semiclassical calculation of photodissociation of the HCl molecule
View Description Hide DescriptionThis paper describes an analytical method to the solution of semiclassical first‐order, time‐dependent coupled equations in the case of a three states process. The method is applied to the study of the photodissociation of the HCl molecule. The results of the semiclassical instantaneous probabilities as function of the interparticle distance are compared with quantum–quantum flux redistribution calculations [M. H. Alexander, B. Pouilly, and T. Duhoo, J. Chem. Phys. 99, 1752 (1993)].