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Multi-state electronic dynamics at higher excitation energies is needed for the understanding of a variety of energy rich situations, including chemistry under extreme conditions, vacuum ultraviolet (VUV) induced astrochemistry, and attochemistry. It calls for an understanding of three stages, energy acquisition, dynamical propagation, and disposal. It is typically not possible to identify a basis of uncoupled quantum states that is sufficient for the three stages. The handicap is the large number of coupled quantum states that is needed to describe the system. Progress in quantum chemistry provides the necessary background to the energetics and the coupling. Progress in quantum dynamics takes this as input for the propagation in time. Right now, it seems that we have come of age with potential detailed applications. We here report a demonstration to a coupled electron-nuclear quantum dynamics through a maze of 47 electronic states and with attention to the order in perturbation theory that is indicated using propensity rules for couplings. Close agreement with experimental results for the VUV photodissociation of 14N2 and its isotopomer 14N15N is achieved. We pay special attention to the coupling between two dissociative continua and an optically accessible bound domain. The computations reproduce and interpret the non-monotonic branching between the two exit channels producing N(2D) and N(2P) atoms as a function of excitation energy and its variation with the mass. [ABSTRACT FROM AUTHOR]

Multi-state electronic dynamics at higher excitation energies is needed for the understanding of a variety of energy rich situations, including chemistry under extreme conditions, vacuum ultraviolet (VUV) induced astrochemistry, and attochemistry. It calls for an understanding of three stages, energy acquisition, dynamical propagation, and disposal. It is typically not possible to identify a basis of uncoupled quantum states that is sufficient for the three stages. The handicap is the large number of coupled quantum states that is needed to describe the system. Progress in quantum chemistry provides the necessary background to the energetics and the coupling. Progress in quantum dynamics takes this as input for the propagation in time. Right now, it seems that we have come of age with potential detailed applications. We here report a demonstration to a coupled electron-nuclear quantum dynamics through a maze of 47 electronic states and with attention to the order in perturbation theory that is indicated using propensity rules for couplings. Close agreement with experimental results for the VUV photodissociation of 14N2 and its isotopomer 14N15N is achieved. We pay special attention to the coupling between two dissociative continua and an optically accessible bound domain. The computations reproduce and interpret the non-monotonic branching between the two exit channels producing N(2D) and N(2P) atoms as a function of excitation energy and its variation with the mass. [ABSTRACT FROM AUTHOR]

The performance of the ring polymer molecular dynamics (RPMD) approach to simulate typical photodissociation processes is assessed. The correct description of photodissociation requires the calculation of correlation functions or expectation values associated with non-equilibrium initial conditions, which was shown to be possible with RPMD very recently [J. Chem. Phys. 145, 204118 (2016)]. This approach is combined with treatment of the nonadiabatic dynamics employing the ring polymer surface hopping approach (RPSH), which is based on Tully's fewest switches surface hopping (FSSH) approach. The performance is tested using one-dimensional photodissociation models. It is found that RPSH with non-equilibrium initial conditions can well reproduce the time-dependent dissociation probability, and adiabatic and diabatic populations for cases where the crossing point is below and above the Franck-Condon point, respectively, while standard FSSH fails to reproduce the exact quantum dynamics in the latter case. Thus, it is shown that RPSH is an efficient and accurate alternative to standard FSSH, which is one of the most widely employed approaches to study photochemistry. [ABSTRACT FROM AUTHOR]

We investigated the effect of the geometric phase (GP) on photodissociation dynamics at a light-induced conical intersection (LICI) through exact quantum dynamical calculations. By taking the one-photon photodissociation of H 2 + ionic molecules as an example, we explored the conditions wherein the LICI associated GP affects dissociation dynamics. We found that GP leads to a phase shift between the angular distributions of GP included and GP excluded photofragments. This effect is more pronounced when the energy of the initial vibrational level is above the energy of the LICI point. [ABSTRACT FROM AUTHOR]

Trajectory surface hopping (TSH) methods have been widely used for the study of nonadiabatic molecular dynamics. In the present work, the accuracy of two TSH algorithms, Tully's fewest switching algorithm and an algorithm based on the Landau-Zener formula, has been critically evaluated in comparison with exact nonadiabatic quantum dynamics calculations for a model of the photoinduced hydrogen-atom dissociation reaction in phenol. The model consists of three electronic states (S0, ¹ππ*, ¹πσ*) and two nuclear degrees of freedom (the OH stretching coordinate and CCOH dihedral angle) and displays two successive conical intersections (¹ππ*/¹πσ* and ¹πσ*/S0). Considering instantaneous photoexcitation from different vibrational levels of the S0 state to the ¹ππ* state, we examined the time-dependent electronic population dynamics as well as the branching ratio of the two dissociation channels. The results of fully converged trajectory calculations are compared with the results of exact quantum wave-packet calculations. It is found that both TSH algorithms describe the dynamics at the ¹πσ*/S0 conical intersection, which is accessed with high excess energy, with good accuracy. The ¹ππ*/¹πσ* conical intersection, on the other hand, is accessed with little excess energy so tunneling effects as well as wave-packet interference effects which cannot be reproduced with classical trajectory calculations become relevant. Overall, the performance of the fewest-switching and Landau-Zener surface-hopping algorithms for the photodissociation of phenol is very similar. The populations of the adiabatic S¹ and S² states are found to exhibit fast oscillations which reflect nonadiabatic electronic transitions driven by coherent dynamics in the OH stretching mode. These electronic population oscillations are qualitatively reproduced by both TSH algorithms. [ABSTRACT FROM AUTHOR]

The singlet electronic potential energy surfaces for the simplest Criegee intermediate CH2OO are computed over a two-dimensional reduced subspace of coordinates, and utilized to simulate the photo-initiated dynamics on the S2 (B) state leading to dissociation on multiple coupled excited electronic states. The adiabatic electronic potentials are evaluated using dynamically weighted stateaveraged complete active space self-consistent field theory. Quasi-diabatic states are constructed from the adiabatic states by maximizing the charge separation between the states. The dissociation dynamics are then simulated on the diabatically coupled excited electronic states. The B<-X electronic transition with large oscillator strength was used to initiate dynamics on the S2 (B) excited singlet state. Diabatic coupling of the B state with other dissociative singlet states results in about 5% of the population evolving to the lowest spin-allowed asymptote, generating H2CO (X¹A1) and O (¹D) fragments. The remaining ~95% of the population remains on repulsive B state and dissociates to H2CO (a³A") and O (³P) products associated with a higher asymptotic limit. Due to the dissociative nature of the B state, the simulated electronic absorption spectrum is found to be broad and devoid of any vibrational structure. [ABSTRACT FROM AUTHOR]

The complex quantum Hamilton-Jacobi equation-Bohmian trajectories (CQHJE-BT) method is introduced as a synthetic trajectory method for integrating the complex quantum Hamilton-Jacobi equation for the complex action function by propagating an ensemble of real-valued correlated Bohmian trajectories. Substituting the wave function expressed in exponential form in terms of the complex action into the time-dependent Schrödinger equation yields the complex quantum Hamilton-Jacobi equation. We transform this equation into the arbitrary Lagrangian-Eulerian version with the grid velocity matching the flow velocity of the probability fluid. The resulting equation describing the rate of change in the complex action transported along Bohmian trajectories is simultaneously integrated with the guidance equation for Bohmian trajectories, and the time-dependent wave function is readily synthesized. The spatial derivatives of the complex action required for the integration scheme are obtained by solving one moving least squares matrix equation. In addition, the method is applied to the photodissociation of NOCl. The photodissociation dynamics of NOCl can be accurately described by propagating a small ensemble of trajectories. This study demonstrates that the CQHJE-BT method combines the considerable advantages of both the real and the complex quantum trajectory methods previously developed for wave packet dynamics. [ABSTRACT FROM AUTHOR]

The primary elimination channel of bromine molecule in one-photon dissociation of CH2BrC(O)Br at 248 nm is investigated using cavity ring-down absorption spectroscopy. By means of spectral simulation, the ratio of nascent vibrational population in v = 0, 1, and 2 levels is evaluated to be 1:(0.5 ± 0.1):(0.2 ± 0.1), corresponding to a Boltzmann vibrational temperature of 581 ± 45 K. The quantum yield of the ground state Br2 elimination reaction is determined to be 0.24 ± 0.08. With the aid of ab initio potential energy calculations, the obtained Br2 fragments are anticipated to dissociate on the electronic ground state, yielding vibrationally hot Br2 products. The temperature-dependence measurements support the proposed pathway via internal conversion. For comparison, the Br2 yields are obtained analogously from CH3CHBrC(O)Br and (CH3)2CBrC(O)Br to be 0.03 and 0.06, respectively. The trend of Br2 yields among the three compounds is consistent with the branching ratio evaluation by Rice-Ramsperger-Kassel-Marcus method. However, the latter result for each molecule is smaller by an order of magnitude than the yield findings. A non-statistical pathway so-called roaming process might be an alternative to the Br2 production, and its contribution might account for the underestimate of the branching ratio calculations. [ABSTRACT FROM AUTHOR]

The speed and angular distribution of O atoms arising from the photofragmentation of C5H8-O2, the isoprene-oxygen van der Waals complex, in the wavelength region of 213-277 nm has been studied with the use of a two-color dissociation-probe method and the velocity map imaging technique. Dramatic enhancement in the O atoms photo-generation cross section in comparison with the photodissociation of individual O2 molecules has been observed. Velocity map images of these 'enhanced' O atoms consisted of five channels, different in their kinetic energy, angular distribution, and wavelength dependence. Three channels are deduced to be due to the one-quantum excitation of the C5H8-O2 complex into the perturbed Herzberg III state (3Δu) of O2. This excitation results in the prompt dissociation of the complex giving rise to products C5H8+O+O when the energy of exciting quantum is higher than the complex photodissociation threshold, which is found to be 41740 ± 200 cm-1 (239.6±1.2 nm). This last threshold corresponds to the photodissociation giving rise to an unexcited isoprene molecule. The second channel, with threshold shifted to the blue by 1480 ± 280 cm-1, corresponds to dissociation with formation of rovibrationally excited isoprene. A third channel was observed at wavelengths up to 243 nm with excitation below the upper photodissociation threshold. This channel is attributed to dissociation with the formation of a bound O atom C5H8-O2 + hv → C5H8-O2(3Δu) → C5H8O + O and/or to dissociation of O2 with borrowing of the lacking energy from incompletely cooled complex internal degrees of freedom C5H8*-O2 + hv → C5H8*-O2(3Δu) → C5H8 + O + O. The kinetic energy of the O atoms arising in two other observed channels corresponds to O atoms produced by photodissociation of molecular oxygen in the excited a 1Δg and b 1Σg+ singlet states as the precursors. This indicates the formation of singlet oxygen O2(a 1Δg) and O2(b 1Σg+) after excitation of the C5H8-O2 complex. Cooperative excitation of the complex with a simultaneous change of the spin of both partners 1X-3O2 + hν → 3X-1O2 → 3X + 1O2 is suggested as a source of singlet oxygen O2(a 1Δg) and O2(b 1Σg+). This cooperative excitation is in agreement with little or no vibrational excitation of O2(a 1Δg), produced from the C5H8-O2 complex as studied in the current paper as well as from the C3H6-O2 and CH3I-O2 complexes reported in our previous paper [Baklanov et al., J. Chem. Phys. 126, 124316 (2007)]. The formation of O2(a 1Δg) from C5H8-O2 was observed at λpump = 213-277 nm with the yield going down towards the long wavelength edge of this interval. This spectral profile is interpreted as the red-side wing of the band of a cooperative transition 1X-3O2 + hν → 3X(T2)-1O2(a 1Δg) in the C5H8-O2 complex. [ABSTRACT FROM AUTHOR]

A recently developed method to represent adiabatic electronic states coupled by conical intersections has been used to construct a full six-dimensional quasi-diabatic representation of the 11A and 21A states of NH3. This representation is expected to be appropriate to simulate the photodissociation of ammonia when it is excited to the 21A electronic state. In this work, the electronic structure aspects of this quasi-diabatic representation are analyzed. This representation is then used as the basis for a simulation of the à ← X absorption spectrum, dominated by a progression in the v2 mode, using a full six-dimensional quantum mechanical treatment of the nuclear motion. Results are reported for both NH3 and ND3. This simulation provides the most accurate computational determination of this absorption spectrum reported to date. These results serve to validate the quasi-diabatic representation and set the stage for subsequent studies of vibrationally mediated photodissociation of NH3. [ABSTRACT FROM AUTHOR]

Photodissociation lifetimes and fragment channels of gas-phase, protonated YAn (n = 1,2) peptides and their dimers were measured with 266 nm photons. The protonated monomers were found to have a fast dissociation channel with an exponential lifetime of ∼200 ns while the protonated dimers show an additional slow dissociation component with a lifetime of ∼2 μs. Laser power dependence measurements enabled us to ascribe the fast channel in the monomer and the slow channel in the dimer to a one-photon process, whereas the fast dimer channel is from a two-photon process. The slow (1 photon) dissociation channel in the dimer was found to result in cleavage of the H-bonds after energy transfer through these H-bonds. In general, the dissociation of these protonated peptides is non-prompt and the decay time was found to increase with the size of the peptides. Quantum RRKM calculations of the microcanonical rate constants also confirmed a statistical nature of the photodissociation processes in the dipeptide monomers and dimers. The classical RRKM expression gives a rate constant as an analytical function of the number of active vibrational modes in the system, estimated separately on the basis of the equipartition theorem. It demonstrates encouraging results in predicting fragmentation lifetimes of protonated peptides. Finally, we present the first experimental evidence for a photo-induced conversion of tyrosine-containing peptides into monocyclic aromatic hydrocarbon along with a formamide molecule both found in space. [ABSTRACT FROM AUTHOR]

A primary dissociation channel of Br2 elimination is detected following a single-photon absorption of (COBr)2 at 248 nm by using cavity ring-down absorption spectroscopy. The technique contains two laser beams propagating in a perpendicular configuration. The tunable laser beam along the axis of the ring-down cell probes the Br2 fragment in the B3Πou+-X1Σg+ transition. The measurements of laser energy- and pressure-dependence and addition of a Br scavenger are further carried out to rule out the probability of Br2 contribution from a secondary reaction. By means of spectral simulation, the ratio of nascent vibrational population for v = 0, 1, and 2 levels is evaluated to be 1:(0.65 ± 0.09):(0.34 ± 0.07), corresponding to a Boltzmann vibrational temperature of 893 ± 31 K. The quantum yield of the ground state Br2 elimination reaction is determined to be 0.11 ± 0.06. With the aid of ab initio potential energy calculations, the pathway of molecular elimination is proposed on the energetic ground state (COBr)2 via internal conversion. A four-center dissociation mechanism is followed synchronously or sequentially yielding three fragments of Br2 + 2CO. The resulting Br2 is anticipated to be vibrationally hot. The measurement of a positive temperature effect supports the proposed mechanism. [ABSTRACT FROM AUTHOR]

The role of triplet states in the UV photodissociation of N2O is investigated by means of quantum mechanical wave packet calculations. Global potential energy surfaces are calculated for the lowest two 3A′ and the lowest two 3A′′ states at the multi-reference configuration interaction level of electronic structure theory using the augmented valence quadruple zeta atomic basis set. Because of extremely small transition dipole moments with the ground electronic state, excitation of the triplet states has only a marginal effect on the far red tail of the absorption cross section. The calculations do not show any hint of an increased absorption around 280 nm as claimed by early experimental studies. The peak observed in several electron energy loss spectra at 5.4 eV is unambiguously attributed to the lowest triplet state 13A′. Excitation of the 21A′ state and subsequent transition to the repulsive branch of the 23A′′ state at intermediate NN-O separations, promoted by spin-orbit coupling, is identified as the main pathway to the N2(1Σg+)+O(3P) triplet channel. The yield, determined in two-state wave packet calculations employing calculated spin-orbit matrix elements, is 0.002 as compared to 0.005 ± 0.002 measured by Nishida et al. [J. Phys. Chem. A 108, 2451 (2004)]. [ABSTRACT FROM AUTHOR]

Accurate full dimensional quantum dynamics calculations studying the photodissociation of CH3I@resorc[4]arene on an ab initio based potential energy surface (PES) model are reported. The converged 189D quantum dynamics calculations are facilitated by the multilayer multi-configurational time-dependent Hartree (ML-MCTDH) approach combined with the correlation discrete variable representation (CDVR) for the evaluation of potential energy matrix elements. The potential employed combines an established ab initio PES describing the photodissociation of methyl iodide in the A band with a harmonic description of the resorc[4]arene host and a bilinear modeling of the host-guest interaction. All potential parameters required in the description of the vibrations of the host molecule and the host-guest interaction are derived from ab initio calculations on the host-guest complex. Absorption spectra at 0 K and 300 K are calculated and the electronic population dynamics during the bond breaking process occurring in the first 20-30 fs after the photoexcitation is investigated. Weak but significant effects resulting from the host-guest interaction on this time scale are found and interpreted. The present study demonstrates that accurate fully quantum mechanical dynamics calculations can be preformed for systems consisting of more than 50 atoms using the ML-MCTDH/CDVR approach. Utilizing an efficient statistical approach for the construction of the ensemble of initial wavepackets, these calculations are not restricted to zero temperature but can also study the dynamics at 300 K. [ABSTRACT FROM AUTHOR]

There has been a substantial amount of theoretical investigations on the photodynamics of pyrrole, often relying on surface hopping techniques or, if fully quantal, confining the study to the lowest two or three singlet states. In this study we extend ab initio based quantum dynamical investigations to cover simultaneously the lowest five singlet states, two π - σ* and two π - π* excited states. The underlying potential energy surfaces are obtained from large-scale MRCI ab initio computations. These are used to extract linear and quadratic vibronic coupling constants employing the corresponding coupling models. For the N-H stretching mode Q24 an anharmonic treatment is necessary and also adopted. The results reveal a sub-picosecond internal conversion from the S4 (π - π*) state, corresponding to the strongly dipole-allowed transition, to the S1 and S2 (π - σ*) states and, hence, to the ground state of pyrrole. The significance of the various vibrational modes and coupling terms is assessed. Results are also presented for the dissociation probabilities on the three lowest electronic states. [ABSTRACT FROM AUTHOR]

We investigated the dynamics of photodissociation of propenal (acrolein, CH2CHCHO) at 157 nm in a molecular beam and of migration and elimination of hydrogen atoms in systems C3H4O and C3H3O using quantum-chemical calculations. Compared with the previous results of photodissociation of propenal at 193 nm, the major difference is that the C3H3O fragment present at the 193-nm photolysis disappears at the 157-nm photolysis whereas the C3H2O fragment absent at 193 nm appears at 157 nm. Optimized structures and harmonic vibrational frequencies of molecular species with gross formula C3H2-4O were computed at the level of B3LYP/6-311G(d,p) and total energies of those molecules at optimized structures were computed at the level of CCSD(T)/6-311+G(3df,2p). Based on the calculated potential-energy surfaces, we deduce that the C3H3O fragment observed in the photolysis of propenal at 193 nm is probably CHCCHOH (2A″) and/or CH2CCOH (2A″) produced from an intermediate hydroxyl propadiene (CH2CCHOH) following isomerization. Adiabatic and vertical ionization potentials of eight isomers of C3H3O and two isomers of C3H2O were calculated; CHCCHOH (2A″) and CH2CCOH (2A″) have ionization potentials in good agreement with the experimental value of ∼7.4 eV. We also deduce that all the nascent C3H3O fragments from the photolysis of propenal at 157 nm spontaneously decompose mainly to C2H3 + CO and C3H2O + H because of the large excitation energy. This work provides profound insight into the dynamics of migration and elimination of hydrogen atoms of propenal optically excited in the vacuum-ultraviolet region. [ABSTRACT FROM AUTHOR]

Full-dimensional quantum mechanical computations are carried out to investigate the photodissociation dynamics of à state NH3 and ND3 using the multiconfiguration time-dependent Hartree (MCTDH) method with recently developed coupled ab initio potential energy surfaces (PESs) [Z. H. Li, R. Valero, and D. G. Truhlar, Theor. Chim. Acc. 118, 9 (2007)]. To use the MCTDH method efficiently the PESs are represented as based on the high-dimensional model representation. The à ← X absorption spectra for both isotopomers were calculated for the zeroth vibrational state of the ground electronic state. With a view to treating larger systems, Jacobi coordinates are used. Computations on the coupled PES are carried out for two-, three-, five-, and six-dimensional model systems to understand the validity of reduced-dimensional calculations. In addition to the fully coupled calculations, the effect of nonadiabatic coupling on absorption spectra is shown by propagating the initial wavepacket only in the à electronic state. The calculated absorption spectra are shown to be in good agreement with available theoretical and experimental observations. Comparisons with calculations using Radau and valence coordinates show the effect of including the symmetry of the system explicitly. Finally, branching ratios for loss of a hydrogen atom via the two available channels are calculated. These predict that the nonadiabatic product increases with the dimension of the calculations and confirm the importance of the full-dimensional calculations. [ABSTRACT FROM AUTHOR]

The energy partitioning in the UV photodissociation of N2O is investigated by means of quantum mechanical wave packet and classical trajectory calculations using recently calculated potential energy surfaces. Vibrational excitation of N2 is weak at the onset of the absorption spectrum, but becomes stronger with increasing photon energy. Since the NNO equilibrium angles in the ground and the excited state differ by about 70°, the molecule experiences an extraordinarily large torque during fragmentation producing N2 in very high rotational states. The vibrational and rotational distributions obtained from the quantum mechanical and the classical calculations agree remarkably well. The shape of the rotational distributions is semi-quantitatively explained by a two-dimensional version of the reflection principle. The calculated rotational distribution for excitation with λ = 204 nm and the translational energy distribution for 193 nm agree well with experimental results, except for the tails of the experimental distributions corresponding to excitation of the highest rotational states. Inclusion of nonadiabatic transitions from the excited to the ground electronic state at relatively large N2-O separations, studied by trajectory surface hopping, improves the agreement at high j. [ABSTRACT FROM AUTHOR]

The significance of conical intersections in photophysics, photochemistry, and photodissociation of polyatomic molecules in gas phase has been demonstrated by numerous experimental and theoretical studies. Optimization of conical intersections of small- and medium-size molecules in gas phase has currently become a routine optimization process, as it has been implemented in many electronic structure packages. However, optimization of conical intersections of small- and medium-size molecules in solution or macromolecules remains inefficient, even poorly defined, due to large number of degrees of freedom and costly evaluations of gradient difference and nonadiabatic coupling vectors. In this work, based on the sequential quantum mechanics and molecular mechanics (QM/MM) and QM/MM-minimum free energy path methods, we have designed two conical intersection optimization methods for small- and medium-size molecules in solution or macromolecules. The first one is sequential QM conical intersection optimization and MM minimization for potential energy surfaces; the second one is sequential QM conical intersection optimization and MM sampling for potential of mean force surfaces, i.e., free energy surfaces. In such methods, the region where electronic structures change remarkably is placed into the QM subsystem, while the rest of the system is placed into the MM subsystem; thus, dimensionalities of gradient difference and nonadiabatic coupling vectors are decreased due to the relatively small QM subsystem. Furthermore, in comparison with the concurrent optimization scheme, sequential QM conical intersection optimization and MM minimization or sampling reduce the number of evaluations of gradient difference and nonadiabatic coupling vectors because these vectors need to be calculated only when the QM subsystem moves, independent of the MM minimization or sampling. Taken together, costly evaluations of gradient difference and nonadiabatic coupling vectors in solution or macromolecules can be reduced significantly. Test optimizations of conical intersections of cyclopropanone and acetaldehyde in aqueous solution have been carried out successfully. [ABSTRACT FROM AUTHOR]

Mass spectra were recorded for (2 + n) resonance enhanced multiphoton ionization (REMPI) of HCl as a function of resonance excitation energy in the 88865-89285 cm-1 region to obtain two-dimensional REMPI data. Band spectra due to two-photon resonance transitions to number of Rydberg states (Ω′ = 0, 1, and 2) and the ion-pair state V(1Σ+(Ω′ = 0)) for H35Cl and H37Cl were identified, assigned, and analyzed with respect to Rydberg to ion-pair interactions. Perturbations show as line-, hence energy level-, shifts, as well as ion signal intensity variations with rotational quantum numbers, J′, which, together, allowed determination of parameters relevant to the nature and strength of the state interactions as well as dissociation and ionization processes. Whereas near-resonance, level-to-level, interactions are found to be dominant in heterogeneous state interactions (ΔΩ ≠ 0) significant off-resonance interactions are observed in homogeneous interactions (ΔΩ = 0). The alterations in Cl+ and HCl+ signal intensities prove to be very useful for spectra assignments. Data relevant to excitations to the j3Σ(0+) Rydberg states and comparison with (3 + n) REMPI spectra allowed reassignment of corresponding spectra peaks. A band previously assigned to an Ω = 0 Rydberg state was reassigned to an Ω = 2 state (ν0 = 88957.6 cm-1). [ABSTRACT FROM AUTHOR]

The photodissociation dynamics of the argon ionized trimer Ar3+ is revisited in the light of recent experimental results of Lepère et al. [J. Chem. Phys. 134, 194301 (2009)], which show that the fragment with little kinetic energy is always a neutral one, thus the available energy is shared by a neutral and ionic fragments as in Ar2+. We show that these results can be interpreted as the photodissociation of the linear isomer of the system. We perform a 3D quantum computation of the vibrational spectrum of the system and study the relative populations of the linear (trimer-core) and perpendicular (dimer-core) isomers. We then show that the charge initially located on the central atom in the ground electronic state of the linear isomer migrates toward the extreme ones in the photoexcitation process such that photodissociation of the linear isomer produces a neutral central atom at rest in agreement with measured product state distributions. [ABSTRACT FROM AUTHOR]

The standard classical expression of the state-resolved photodissociation cross section is not consistent with an efficient Bohr quantization of product internal motions. A new and strictly equivalent expression not suffering from this drawback is proposed. This expression opens the way to more realistic classical simulations of direct polyatomic photodissociations in the quantum regime where only a few states are available to the products. [ABSTRACT FROM AUTHOR]

The photodissociation dynamics of H2O via the C state by two-photon excitation has been investigated using the H atom Rydberg tagging time-of-flight technique. The rotational resolved action spectrum of the C←X transition band has been measured. The line widths show a pronounced dependence on the parent rotational excitation in the C state. The quantum state resolved OH product translational energy distributions and angular distributions have also been obtained. By carefully simulating these distributions, quantum state distributions of the OH product as well as the state-resolved angular anisotropy parameters were determined. The experimental results confirm the variation of two competitive predissociation pathways. A heterogeneous predissociation channel is mediated by rotational coupling to the B 1A1 state associated with the a-axis (ka′), and a homogeneous pathway arises from purely electronic coupling to the à 1B1 state. We have also obtained the branching ratios of the OH(X) and OH(A) products, and related these to the C→à and C→B pathways. The branching ratios display a strong ka′ dependence. [ABSTRACT FROM AUTHOR]

The lowest five 1A′ states of ozone, involved in the photodissociation with UV light, are analyzed on the basis of multireference configuration interaction electronic structure calculations with emphasis on the various avoided crossings in different regions of coordinate space. Global diabatic potential energy surfaces are constructed for the lowest four states termed X, A, B, and R. In addition, the off-diagonal potentials that couple the initially excited state B with states R and A are constructed to reflect results from additional electronic structure calculations, including the calculation of nonadiabatic coupling matrix elements. The A/X and A/R couplings are also considered, although in a less ambitious manner. The photodissociation dynamics are studied by means of trajectory surface hopping (TSH) calculations with the branching ratio between the singlet, O(1D)+O2(1Δg), and triplet, O(3P)+O2(3Σg-), channels being the main focus. The semiclassical branching ratio agrees well with quantum mechanical results except for wavelengths close to the threshold of the singlet channel. The calculated O(1D) quantum yield is approximately 0.90–0.95 across the main part of the Hartley band, in good agreement with experimental data. TSH calculations including all four states show that transitions B→A are relatively unimportant and subsequent transitions A→X/R to the triplet channel are negligible. [ABSTRACT FROM AUTHOR]

The 3D photodissociation dynamics of HCl and HF molecules adsorbed on ice is studied by quantum and classical simulations. The quantum calculations are carried out with the multiconfiguration time-dependent Hartree (MCTDH) approach. Dynamical observables like angular distributions in the momentum space of the H fragments, absorption cross sections are computed. The results are compared with our previous 2D studies. As expected, less encapsulation of the H atom between the ice surface and the halogen atom is obtained in the 3D study, resulting in less pronounced interference structures in the photoabsorption cross sections and in a decrease of the classical rainbow peaks observed in the 2D scheme. Although the amplitudes of the oscillations corresponding to quantum interferences in the asymptotic angular distribution of the H fragment are different between the 2D and 3D results, the qualitative pattern of the oscillations is similar in the 2D and 3D approaches. In addition, a good agreement is observed for the angular distribution between the classical and the quantum calculations. [ABSTRACT FROM AUTHOR]

The mechanisms of radiationless decay involved in the photodissociation of formaldehyde into H2 and CO have been investigated using complete active space self-consistent field (CASSCF) calculations and direct dynamics variational multiconfiguration Gaussian (DD-vMCG) quantum dynamics in the S1, T1, and S0 states. A commonly accepted scheme involves Fermi Golden Rule internal conversion from S1 followed by dissociation of vibrationally hot H2CO in S0. We recently proposed a novel mechanism [M. Araujo et al., J. Phys. Chem. A 112, 7489 (2008)] whereby internal conversion and dissociation take place in concert through a seam of conical intersection between S1 and S0 after the system has passed through an S1 transition barrier. The relevance of this mechanism depends on the efficiency of tunneling in S1. At lower energy, an alternative scheme to internal conversion involves intersystem crossing via T1 to regenerate the reactant before the S0 barrier to dissociation. We propose here a previously unidentified mechanism leading directly to H2 and CO products via T1. This channel opens at medium energies, near or above the T1 barrier to dissociation and still lower than the S1 barrier, thus making T1 a possible shortcut to molecular dissociation. [ABSTRACT FROM AUTHOR]

In concert with the latest experiment of velocity imaging technique [X. P. Zhang et al., ChemPhysChem 9, 1130 (2008)], quantum chemical calculations with relativistic effect were performed on the photodissociation of bromobenzene (BrPh) and iodobenzene (IPh) at 266 nm. The method of multistate second order multiconfigurational perturbation theory in conjunction with spin-orbit interaction through complete active space state interaction was employed to calculate the potential energy curves for the ground and low-lying excited states of BrPh and IPh along their photodissociation reaction coordinates. The dissociation mechanisms with products of X(2P3/2) and X*(2P1/2) (X=Br,I) states were clarified. [ABSTRACT FROM AUTHOR]

The degree to which tunneling through a barrier in the N–H and N–D photodissociation channels of methylamine (CH3NH2) and its deuterated variant (CH3ND2), respectively, plays a role was investigated by time-dependent quantum wave-packet dynamics calculations. Two dimensional potential energy surfaces (PESs) of methylamine, presenting the N–H stretch and the HNC bend, were constructed employing multireference ab initio electronic-structure methods, allowing full description of the H motion on the HC–NH2 plane. The time-dependent Schrödinger equation was solved employing the Fourier method for calculating the Hamiltonian operation together with the Chebychev polynomial expansion of the evolution operator. The results show that tunneling and decay to vibrational resonant states on the first excited electronic PES are faster for the H atom than for the D. The decay into two of the resonant states found on the first PES strongly depends on the initially excited vibrational state on the ground electronic PES. [ABSTRACT FROM AUTHOR]

The degree to which tunneling through a barrier in the N–H and N–D photodissociation channels of methylamine (CH3NH2) and its deuterated variant (CH3ND2), respectively, plays a role was investigated by time-dependent quantum wave-packet dynamics calculations. Two dimensional potential energy surfaces (PESs) of methylamine, presenting the N–H stretch and the HNC bend, were constructed employing multireference ab initio electronic-structure methods, allowing full description of the H motion on the HC–NH2 plane. The time-dependent Schrödinger equation was solved employing the Fourier method for calculating the Hamiltonian operation together with the Chebychev polynomial expansion of the evolution operator. The results show that tunneling and decay to vibrational resonant states on the first excited electronic PES are faster for the H atom than for the D. The decay into two of the resonant states found on the first PES strongly depends on the initially excited vibrational state on the ground electronic PES. [ABSTRACT FROM AUTHOR]

Infrared photodissociation (IRPD) spectra of [H2O•(CO2)n]+ and [CH3OH•(CO2)n]+ (n=1–7) are measured in the 1100–3800 cm-1 region. At the same time, the solvation characteristics in the clusters are investigated theoretically; the geometry optimization and the vibrational analysis are carried out for the [H2O•(CO2)n]+ (n=1–4) and the [CH3OH•(CO2)n]+ (n=1–3) ions at the MP2/6-31+G* level of theory. The IRPD spectrum of the [H2O•(CO2)1]+ ion shows the free OH and the hydrogen-bonded OH stretching bands of the H2O+ ion core and the antisymmetric CO stretching band of the solvent CO2 molecule, indicating that the solvent CO2 molecule is preferentially solvated to the H2O+ ion core via the O–H•••OCO hydrogen bond. In [H2O•(CO2)2]+, the free OH stretching band is not observed; both of the OH groups of the H2O+ ion core are hydrogen bonded to the solvent CO2 molecules. Spectral features of the IRPD spectra of [H2O•(CO2)n]+ (n=3–7) suggest that the third and the fourth CO2 molecules are bound to the oxygen atom of the H2O+ ion core, and that the first solvation shell of the H2O+ ion core becomes filled with four CO2 molecules. All the IRPD spectra of the [CH3OH•(CO2)n]+ (n=1–7) ions display the hydrogen-bonded OH stretching band of the CH3OH+ ion core, meaning that the solvent CO2 molecule is preferentially bonded to the OH group of the CH3OH+ ion core, similar to the case of [H2O•(CO2)n]+. Quantum chemical calculations for the [CH3OH•(CO2)1–3]+ ions demonstrate that the second and the third solvent CO2 molecules are bonded to the oxygen atom of the CH3OH+ ion core. [ABSTRACT FROM AUTHOR]

Atomic sulfur products from predissociation of the lowest rotational states of SH/SD A 2Σ+ (v′=0,1,2) are studied using velocity map imaging. The dissociation process, which is slow compared to rotation, is dominated by interference effects due to predissociation of states with low rotation quantum numbers prepared by photoexcitation using overlapping transitions of different parities. The measured product angular distributions can be modeled using the methods presented recently by Kim et al. [J. Chem. Phys. 125, 133316 (2006)]. The S(3PJ) (2+1) resonance enhanced multiphoton ionization scheme used in the detection step of the experiment is sensitive to the angular momentum polarization of the atomic fragments. S(3PJ), J=2,1,0, fine-structure yields, angular distributions, and atom polarization parameters are reported. Strong polarization of the S(3P2,1) products was observed along with a weak sensitivity of the branching ratio to excess energy and a full insensitivity of the atomic product polarization to excess energy. None of the data fit the predictions of either adiabatic or diabatic photodissociation, emphasizing the need for a fully quantum treatment. [ABSTRACT FROM AUTHOR]

Full-dimensional quantum dynamics of the Ã-state photodissociation of NH3 and ND3 is characterized on potential energy surfaces recently developed by Li et al. [Theor. Chem. Acc. 118, 9 (2007)]. The Ã←X absorption spectra of the two isotopomers were obtained for several vibrational levels on the ground electronic state. The calculated positions and lifetimes of low-lying umbrella resonances on the excited à electronic state are found to reproduce experimental trends and shed light on the multidimensional dynamics. The agreement with measured spectra is reasonable, but assignment of some individual features remains incomplete. [ABSTRACT FROM AUTHOR]

We present a dc sliced ion imaging study of HCCO radical photodissociation to CH and CO at 230 nm. The measurements were made using a two-color reduced Doppler probe strategy. The CO rotational distribution was consistent with a Boltzmann distribution at 3500 K. Using the dc slice ion imaging approach, we obtained CO images for various rotational levels of CO (v=0). The results are largely consistent with earlier work, albeit with a significant 0.9 eV peak seen previously in the translational energy distributions absent in our state-selected imaging study. [ABSTRACT FROM AUTHOR]

The photodissociation of rotationally state-selected methyl bromide is studied in the wavelength region between 213 and 235 nm using slice imaging. A hexapole state selector is used to focus a single (JK=11) rotational quantum state of the parent molecule, and a high speed slice imaging detector measures directly the three-dimensional recoil distribution of the methyl fragment. Experiments were performed on both normal (CH3Br) and deuterated (CD3Br) parent molecules. The velocity distribution of the methyl fragment shows a rich structure, especially for the CD3 photofragment, assigned to the formation of vibrationally excited methyl fragments in the ν1 and ν4 vibrational modes. The CH3 fragment formed with ground state Br(2P3/2) is observed to be rotationally more excited, by some 230–340 cm-1, compared to the methyl fragment formed with spin-orbit excited Br(2P1/2). Branching ratios and angular distributions are obtained for various methyl product states and they are observed to vary with photodissociation energy. The nonadiabatic transition probability for the 3Q0+→1Q1 transition is calculated from the images and differences between the isotopes are observed. Comparison with previous non-state-selected experiments indicates an enhanced nonadiabatic transition probability for state-selected K=1 methyl bromide parent molecules. From the state-to-state photodissociation experiments the dissociationenergy for both isotopes was determined, D0(CH3Br)=23 400±133 cm-1 and D0(CD3Br)=23 827±94 cm-1. [ABSTRACT FROM AUTHOR]

Multireference spin-orbit configuration interaction calculations of transition moments from the X A1 ground state to the 3Q0+, 3Q1, and 1Q excited states responsible for the A absorption band of CH3I are reported and employed for an analysis of the photofragmentation in this system. Contrary to what is usually assumed, the 3Q0+(A1), 3Q1(E), and 1Q(E)←X A1 transition moments are found to be strongly dependent on the C–I fragmentation coordinate. The sign of this dependence is opposite for the parallel and perpendicular transitions, which opens an opportunity for vibrational state control of the photodissociation product yields. The computed absorption intensity distribution and the I* quantum yield as a function of excitation energy are analyzed in comparison with existing experimental data, and good agreement between theory and experiment is found. It is predicted that significantly higher I* quantum yield values (>0.9) may be achieved when vibrationally hot CH3I molecules are excited in the appropriate spectral range. It is shown that vibrational state control of the I*/I branching ratio in the alkyl (hydrogen) iodide photodissociation has an electronic rather than a dynamic nature: Due to a different electron density distribution at various molecular geometries, one achieves a more efficient excitation of a particular fragmentation channel rather than influences the dynamics of the decay process. [ABSTRACT FROM AUTHOR]

Optimal control simulation is used to examine the control mechanisms in the photodissociation of phenol within a two-dimensional, three-electronic-state model with two conical intersections. This model has two channels for H-atom elimination, which correspond to the 2π and 2σ states of the phenoxyl radical. The optimal pulse that enhances 2σ dissociation initially generates a wave packet on the S1 potential-energy surface of phenol. This wave packet is bifurcated at the S2-S1 conical intersection into two components with opposite phases because of the geometric phase effect. The destructive interference caused by the geometric phase effect reduces the population around the S1-S0 conical intersection, which in turn suppresses nonadiabatic transitions and thus enhances dissociation to the 2σ limit. The optimal pulse that enhances S0 dissociation, on the other hand, creates a wave packet on the S2 potential-energy surface of phenol via an intensity borrowing mechanism, thus avoiding geometric phase effects at the S2-S1 conical intersection. This wave packet hits the S1-S0 conical intersection directly, resulting in preferred dissociation to the 2π limit. The optimal pulse that initially prepares the wave packet on the S1 potential-energy surface (PES) has a higher carrier frequency than the pulse that prepares the wave packet on the S2 PES. This counterintuitive effect is explained by the energy-level structure and the S2-S1 vibronic coupling mechanism. [ABSTRACT FROM AUTHOR]

The electronically excited states HCl*(E,υ′=0,J′=0) and HCl*(V,υ′=12,J′=0) have been prepared by two-photon resonant absorption of ground state HCl via Q(0) transitions at 238.719 and at 236.000 nm, respectively. The consequent one-or two-photon excitation at the same wavelength results in the production of H+, Cl+, and HCl+ ions. The speed distributions and anisotropy parameters β for these ions have been determined by three-dimensional photofragment ion imaging based on a position-sensitive delay-line anode assembly. Several results are presented: first, we measured velocity (speed and angle) distributions for HCl+ due to the electron recoil in the photoionization of HCl*. Such distributions give information on the photoionization process and on the vibrational distribution of HCl+ after the laser pulse. Second, the measured β parameters for Cl+ and H+ distributions give information on the symmetries of the upper states in the one-photon photoexcitation of HCl*. Third, the measured speed distributions for H+ help to understand the mechanism of the photodissociation of HCl+ ions. [ABSTRACT FROM AUTHOR]

Coherent phase control of the photodissociation reaction of the dimethylsulfide has been achieved by means of quantum-mechanical interference between one- and three-photon transitions. Dimethylsulfide was irradiated by fundamental and frequency-tripled outputs of a visible laser (600.5–602.5 nm), simultaneously to yield CH3S+ and CH3SCH2+ fragment ions. The branching ratio of the two product channels could be modulated with variation of the phase difference between the light fields. This accounted for the difference between the molecular phases of the two product channels. The phase lag was observed to have a maximum value of 8° at 601.5 nm. This is the first result of a selective bond breaking in a polyatomic molecule by the coherent phase control. [ABSTRACT FROM AUTHOR]

In a recent paper [D. Babikov, J. Chem. Phys. 121, 7577 (2004)], quantum optimal control theory was applied to analyze the accuracy of quantum gates in a quantum computer based on molecular vibrational eigenstates. The effects of the anharmonicity parameter of the molecule, the target time of the pulse, and the penalty function on the accuracy of the qubit transformations were investigated. We demonstrate that the effects of all the molecular and laser-pulse parameters can be explained utilizing the analytical pulse area theorem, which originates from the standard two-level model. Moreover, by analyzing the difference between the optimal control theory results and those obtained using the pulse area theorem, it is shown that extremely high quantum gate fidelity can be achieved for a qubit system based on vibrational eigenstates. [ABSTRACT FROM AUTHOR]

We present a novel quantum-dynamics approach suitable for computing direct dissociation processes, including electronic transitions. This approach combines quantum trajectories in the Lagrangian reference frame with standard fixed-grid wave packets in order to overcome the limitations and difficulties of both techniques. As a model application, we consider the ultrafast photodissociation of H2 excited by a femtosecond extreme UV laser pulse. [ABSTRACT FROM AUTHOR]

Three-dimensional diabatic potential energy surfaces for the lowest four electronic states of ozone with 1A′ symmetry—termed X, A, B, and R—are constructed from electronic structure calculations. The diabatization is performed by reassigning corresponding energy points. Although approximate, these diabatic potential energy surfaces allow one to study the uv photodissociation of ozone on a level of theory not possible before. In the present work photoexcitation in the Hartley band and subsequent dissociation into the singlet channel, O3(X)+hν→O(1D)+O2(a 1Δg), are investigated by means of quantum mechanical and classical trajectory calculations using the diabatic potential energy surface of the B state. The calculated low-resolution absorption spectrum as well as the vibrational and rotational state distributions of O2(a 1Δg) are in good agreement with available experimental results. [ABSTRACT FROM AUTHOR]

The title theory is developed by combining the Herman-KIuk semiclassical theory for adiabatic propagation on single potential-energy surface and the semiclassical Zhu-Nakamura theory for nonadiahatic transition. The formulation with use of natural mathematical principles leads to a quite simple expression for the propagator based on classical trajectories and simple formulas are derived for overall adiabatic and nonadiahatic processes. The theory is applied to electronically nonadiahatic photodissociation processes: a one-dimensional problem of HY in a cw (continuous wave) laser field and a two-dimensional model problem of H2O in a cw laser field. The theory is found to work well for the propagation duration of several molecular vibrational periods and wide energy range. Although the formulation is made for the case of laser induced nonadiahatic processes, it is straightforwardly applicable to ordinary electronically nonadiahatic chemical dynamics. [ABSTRACT FROM AUTHOR]

High-resolution IR-UV multiple resonance methods are employed to elucidate the photodissociation dynamics of quantum state-selected Ar–HOD and Ar–H2O van der Waals clusters. A single mode pulsed OPO operating in the region of the OH second overtone is used to prepare individual rovibrational states that are selectively photodissociated at specific excimer wavelengths. Subsequent fluorescence excitation of the resulting OH (OD) fragments yields dynamical information on the photofragmentation event and any resulting intracluster collisions. This technique is used to characterize spectroscopically the Π(101), vOH=3←Σ(000), vOH=0 overtone band of the Ar–HOD complex with an origin at 10648.27 cm-1. The effects of Ar complexation on the dissociation dynamics are inferred by comparison of the OD photofragment quantum state distributions resulting from dissociation of single rovibrational states of the complex with those from isolated HOD photodissociation. The important role played by the initial internal state of the complex is demonstrated by comparison of the current Ar–HOD data with previously published results for the Ar–H2O Σ(000)|03-> state. We interpret the dramatic differences in the dynamics of the two systems as manifestations of the nodal structure of the vibrational state in the parent complex and the way in which it governs the collision probability between the Ar atom and the escaping photofragments. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report polarization spectroscopy of oriented gas phase nitroaromatic compounds, specifically nitrobenzene and the three isomers of nitrotoluene. Orientation of supersonically cooled molecules was achieved in a uniform electric field. The dependence of the yield of NO on the polarization direction of the excitation laser was used to derive the direction of the transition dipole. The transition to the S[SUB2] state centered at 250 nm demonstrated increased yield when the excitation laser was polarized perpendicular to the orientation field. The transition dipole was therefore characterized to be near perpendicular to the permanent dipole. The transition to S[SUB3] showed an opposite behavior, indicating that the transition dipole for S[SUB3] is primarily parallel to the permanent dipole. Quantitative analysis of the polarization dependence further revealed that in both cases, the transition dipole is not strictly parallel or perpendicular to the permanent dipole, and the tilt is about 20°-30°. This result demonstrates the sophisticated nature of electronically excited states of nitroaromatics. It is therefore not surprising that only two previous theoretical calculations agree with our results, while other calculations and experimental work in condensed phases do not. [ABSTRACT FROM AUTHOR]

The quantum treatment of the photodissociation of aligned, vibrationally excited molecules prepared by polarized laser excitation is presented. A formal expression for the angle-dependent multipole moments of a photofragment is derived. As a specific example, the projection of the laboratory angular distribution (zero-order moment) along a probe direction is considered, and Doppler-shift-dependent fluxes for various arrangements of the polarization directions of the vibrational excitation and photolysis lasers are computed. The profiles depend upon the photodissociation dynamics only through the conventional recoil anisotropy parameter β, as in one-photon dissociation. More generally, the dynamical information obtainable from measurement of vector correlations in VMP is the same as that which can be extracted in a one-photon dissociation experiment. Nevertheless, measurement of vector correlations for vibrationally mediated photodissociation can provide new information on the dissociation dynamics since different regions of the excited potential energy surface(s) are accessed from those accessed in one-photon dissociation. [ABSTRACT FROM AUTHOR]

The photodissociations of jet-cooled IBr and Br[sub 2] molecules have been investigated using high resolution ion imaging methods, at excitation energies just above the thresholds for forming, respectively, I(²P[sup o,sub 3/2])+Br(²P[sup o,sub 3/2]) and Br(²P[sup o,sub 3/2])+Br[sup *](²P[sup o,sub ½]) products from parent molecules in their ν' = 0 levels. For such molecules, we observe in both cases, that fragments with larger recoil velocities have markedly reduced angular anisotropy, whereas those from photolysis of IBr molecules with ν' = l show an essentially constant, limiting anisotropy. Given the monochromaticity of the photolysis radiation, increased recoil velocity of fragments resulting from photolysis of ν' = 0 molecules can only be derived from increased parent internal (rotational) energy. The measurements thus provide a particularly clear and direct observation of the breakdown of the axial recoil approximation as applied to the photodissociation of a diatomic molecule, and have been modeled, quantitatively, using both quantum and semiclassical methods together with the best available potential energy curves for the relevant excited states of IBr and Br[sub 2]. [ABSTRACT FROM AUTHOR]

Examines the photodissociation of water in the first absorption band. Impact of the process on the excitation of the first triplet state; Application of quantum mechanical methods in the calculation of potential-energy surface; Need for a comparison between measurement and absorption spectra levels and water photodissociation.

Quantum mechanical analysis is presented for the alignment of the oxygen atoms produced from the photodissociation of OH. The alignment parameters are predicted to be independent of energy across the isolated Lorentzian resonances, when only one channel contributes to indirect dissociation. When more than one channel interferes with one another, they may change very slowly. Across the asymmetric resonances, the alignments exhibit rapid variations due to the quantum interference between the indirect and the direct dissociation pathways. The alignments of O([SUP3]P[SUB2])and O([SUP3]P[SUB1])exhibit different variations, both of which are asymmetric across the asymmetric resonances. It is also shown that photoexcitation to repulsive states, coupled with bound electronic states, can give asymmetric resonances and sharp variations of the alignment, suggesting that the analysis of the dynamics of direct photodissociation by measurements of vector properties could be complicated by the effects of quantum interference. [ABSTRACT FROM AUTHOR]

Quantum mechanical analysis is presented on the vibrational state dependence of the total dissociation cross sections and the branching ratios of O(3Pj, j=0,1,2) in the predissociation of OH. Two transformation matrices, each of which describes the relation between an atomic term limit and the correlating molecular states, are constructed and incorporated in the close coupling calculations. The branching ratios of O(3Pj, j=0,1,2) depend very sensitively on the vibrational levels (v=0–4) of the initial X 2Π state. The variations of the spin–orbit distributions as a function of the excitation energy near the asymmetric resonances change markedly depending on the vibrational levels. The variations are either redshifted or blueshifted from the resonance position, depending on the degree of asymmetry of the resonances. The widths of the variations tend to increase with increasing vibrational quantum number of the initial state, suggesting the possibility of choosing the proper linewidths in the experiments to selectively produce the photofragments in one-photon process. Discussion is presented on the applicability of the theoretical scheme to analyze the recent measurements by Neumark and co-workers [J. Chem. Phys. 103, 2495 (1995)] on the product fine structure distributions in the predissociation of O2. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this work, we examine the validity of a hybrid quantum/classical method used to study the photodissociation/recombination dynamics of I2(A) in rare gas matrices. Our simplified model includes a I2 molecule embedded in a linear chain of rare gas atoms (Kr or Xe). The aggregate is partitioned into a quantum system and a classical bath and their dynamics are coupled self-consistently within the Ehrenfest framework. Two partitioning schemes are used. The first scheme treats the I–I coordinate quantum mechanically and the rare gas coordinates classically. The second and more reliable scheme includes in the quantum system both the I–I mode and the symmetric motion of the two nearest rare gas atoms. Both models show substantial energy transfer from the dissociating iodine to the solvent, followed by coherent vibrational motion in the recombined I2. It is found that the one-dimensional quantum/classical scheme is consistent with its higher dimensional counterpart, although the latter shows much faster dephasing. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]