Nonadiabatic calculations of ultraviolet absorption cross section of sulfur monoxide: isotopic effects on the photodissociation reaction.

Ultraviolet absorption cross sections of the main and substituted sulfur monoxide (SO) isotopologues were calculated using R-Matrix expansion technique. Energies, transition dipole moments, and nonadiabatic coupling matrix elements were calculated at MRCI/AV6Z level. The calculated absorption cross section of (32)S(16)O was compared with experimental spectrum; the spectral feature and the absolute value of photoabsorption cross sections are in good agreement. Our calculation predicts a long lived photoexcited SO* species which causes large non-mass dependent isotopic effects depending on the excitation energy in the ultraviolet region.

Isomerization reaction between linear AlNC and AlCN including the X 1Σ+ and à 1Π states studied by three-dimensional wave packet propagation.

Excitation transfers between linear AlNC and AlCN via the à (1)Π (1 (1)A", 2 (1)A')-X (1)Σ(+) transition were studied by a wave packet propagation method as applied to a simple system for an isomerization reaction. The photoabsorption and fluorescence spectra calculated in this work are in good agreement with Einstein's A and B coefficients reported in our previous paper [I. Tokue and S. Nanbu, J. Chem. Phys. 124, 224301 (2006)]. In the 2 (1)A'-X (1)Σ(+) excitation of linear AlNC, both isomerization to linear AlCN and dissociation to Al + CN can occur; the probability of both decay channels strongly depends on the vibrational modes of the initial wave packet. The 1 (1)A"-X (1)Σ(+) excitation of linear AlNC results primarily in dissociation with isomerization being found to be a relatively minor phenomenon. For the linear AlCN excitation, vibrational levels above 1000 cm(-1) occur for both isomerization and dissociation. The isomerization of AlNC ↔ AlCN was found to occur after the à (1)Π-X (1)Σ(+) fluorescence of AlNC and AlCN, with even the initial wave packet being made with the vibrational ground level of the à (1)Π state, whereas no dissociation was recognized for any of the cases calculated in this study using lower vibrational levels as initial wave packets. The procedure for wave packet propagation employed in this study is concluded to be very effective for analyzing in detail the reaction dynamics of isomerization for triatomic molecules.

Theoretical studies of absorption cross sections for the C (1)B(2)-X (1)A(1) system of sulfur dioxide and isotope effects.

The C (1)B(2)-X (1)A(1) photoexcitation of SO(2) was studied to investigate excited-state dynamics and the effects of the initial vibrational state. Ultraviolet photoabsorption cross sections (sigma's) of seven isotopologues ((32)S (16)O(2), (33)S (16)O(2), (34)S (16)O(2), (36)S (16)O(2), (32)S(16)O(17)O, (32)S(16)O(18)O, (34)S(16)O(18)O) were computed using the wave packet propagation technique based on the three-dimensional potential energy surfaces of the X and C states, which were calculated using the ab initio molecular orbital configuration interaction method. Numerous wave packet simulations were carried out under the adiabatic approximation and used to calculate the sigma's of the seven isotopologues at 298 K; we concluded that the absorption spectrum of SO(2) can be reliably modeled within the adiabatic framework based on the analysis of the time evolution of the wave packet. The calculated sigma's are in reasonable agreement with the recent experiment in the 190-228 nm region, and the isotope shifts of the peaks for (33)S (16)O(2) and (34)S (16)O(2) relative to the corresponding peaks for (32)S (16)O(2) are in good agreement with the observed data. Relative to the sigma of (32)S (16)O(2), isotopic substitution shows a significant increment for those of (34)S (16)O(2) and (36)S (16)O(2) in the 190-228 nm region. This trend is consistent with the observed data.

Kinetic study of vibrational energy transfer from a wide range of vibrational levels of O2(X(3)Sigma(g)-, v = 6-12) to CF4.

A wide range of vibrational levels of O2(X(3)Sigma(g)(-), v = 6-13) generated in the ultraviolet photolysis of O3 was selectively detected by the laser-induced fluorescence (LIF) technique. The time-resolved LIF-excited B(3)Sigma(u)(-)-X(3)Sigma(g)(-) system in the presence of CF4 has been recorded and analyzed by the integrated profiles method (IPM). The IPM permitted us to determine the rate coefficients k(v)(CF4) for vibrational relaxation of O2(X(3)Sigma(g)(-), v = 6-12) by collisions with CF4. Energy transfer from O2 (v = 6-12) to CF4 is surprisingly efficient compared to that of other polyatomic relaxation partners studied so far. The k(v)(CF4) increases with vibrational quantum number v from [1.5 +/- 0.2(2sigma)] x 10(-12) for v = 6 to [7.3 +/- 1.5(2sigma)] x 10(-11) for v = 12, indicating that the infrared-active nu3 vibrational mode of CF4 mainly governs the energy transfer with O2(X(3)Sigma(g)(-), v = 6-12). The correlation between the rate coefficients and fundamental infrared intensities has been discussed based on a comparison of the efficiency of energy transfer by several collision partners.

Vibrational relaxation of O2(X3 Sigma g-, v = 9-13) by collisions with O2.

Vibrationally excited O(2)(X(3) Sigmag(-)) was generated in the UV laser flash photolysis of O(3) and single vibrational level was detected via laser-induced fluorescence (LIF) in the B(3) Sigmau(-)-X(3) Sigmag(-) system. The time-resolved LIF of adjacent vibrational levels has been analyzed by the integrated-profiles method and the rate coefficients for single-quantum relaxation, O(2)(X(3)Sigmag(-), v = 9-13)+ O(2)(v = 0)--> O(2)(X(3)Sigmag(-), v - 1)+ O(2)(v = 1), have been determined. To the best of our knowledge, the rate coefficients for v = 12 and 13 are measured for the first time in the present study. The efficiency of relaxation is higher at lower vibrational levels, indicating that a small energy mismatch is suitable for the energy transfer. The vibrational level dependence of all the rate coefficients for the relaxation measured in the present study and previously reported by several groups can be rationalized by the energy gap law.

The vibrational structure of the X 1A1 - A 1B1 and A 1B1 - B 1A1 band systems of GeH2/GeD2 based on global potential energy surfaces.

Transition probabilities were evaluated for the X (1)A(1)-A (1)B(1) and A (1)B(1)-B (1)A(1) systems of GeH(2) and GeD(2) to analyze the X-->A-->B photoexcitation. Franck-Condon factors (FCFs) and Einstein's B coefficients were computed by quantum vibrational calculations using the three-dimensional potential energy surfaces (PESs) of the X (1)A(1), A (1)B(1), and B (1)A(1) electronic states and the transition dipole moments for the X-A and A-B systems. The global PESs were determined by the multireference configuration interaction calculations with the Davidson correction and the interpolant moving least squares method combined with the Shepard [Proceedings of the 1968 23rd ACM National Conference (ACM, New York, 1968)] interpolation. The barriers to linearity correcting the spin-orbit interaction are evaluated to be 22,000 cm(-1) for the X state, 6300 cm(-1) for the A state, and 560 cm(-1) for the B state. The obtained FCFs for the X-A and A-B systems indicate that the bending mode is strongly enhanced in the excitation since the equilibrium bond angle greatly varies within the three states. The photoexcitation and fluorescence spectra calculated for the X-A system agree well with the observed spectra. The theoretical lifetimes for lower vibrational levels of the A and B states were calculated from the fluorescence decay rates for the A-X, B-A, and B-X emissions, and the lifetimes for the A state are in good agreement with the observed values except those affected by predissociation.

Quenching and vibrational relaxation of SO(B3Sigma-, v'

Fluorescence from a single vibronic level of SO(B3Sigma-, v'

Theoretical transition probabilities for the A 1Pi-X 1Sigma+ system of AlNC and AlCN isomers based on global potential energy surfaces.

Transition probabilities were evaluated for the X (1)Sigma(+)-A (1)Pi system of AlNC and AlCN isomers to analyze photoabsorption and fluorescence spectra. The global potential energy surfaces (PESs) of the X (1)Sigma(+) and A (1)Pi (1 (1)A("),2 (1)A(')) electronic states were determined by the multireference configuration interaction calculations with the Davidson correction. Einstein's B coefficients were computed by quantum vibrational calculations using the three-dimensional PESs of these states and the electronic transition moments for the X-1 (1)A(") and X-2 (1)A(') systems. Einstein's B coefficients obtained for AlNC or AlCN exhibit that the Al-N or Al-C stretching mode is strongly enhanced in the transition. The absorption and fluorescence spectra calculated for the X-1 (1)A(") and X-2 (1)A(') systems are discussed comparing with the observed photoexcitation and fluorescence spectra. The lifetimes for the several vibrational levels of the A (1)Pi state were calculated to be ca. 7 ns for AlNC and 21-24 ns for AlCN from the fluorescence decay rates of the 1 (1)A(")-X and 2 (1)A(')-X emissions.

Efficient vibrational relaxation of O2(X 3sigma(g)-, nu = 8) by collisions with CF4.

A laser flash photolysis-laser-induced fluorescence (LIF) technique has been employed to study the relaxation kinetics of vibrationally excited O2(X 3sigma(g)-. The time-resolved LIF excited B 3sigma(u)(-)-X 3sigma(g)- system has been recorded and analyzed by the integrated-profiles method. The rate coefficient for vibrational relaxation of O2(X 3sigma(g)-, nu = 8) by collisions with CF(4), [1.4 +/- 0.3(2sigma)] x 10(-11) cm3 molecule(-1) s(-1), indicates that CF4 is an efficient relaxant of O2(X 3sigma(g)- and that the propensity rule for O2 relaxation suggested by Mack et al. (J. A. Mack, K. Mikulecky and A. M. Wodtke, J. Chem. Phys., 1996, 105, 4105) has been observed experimentally.

Isotope effects in the dissociation of the B 1A1 state of SiH2, SiHD, and SiD2 using three-dimensional wave packet propagation.

Dissociations after the A 1B1-->B 1A1 photoexcitation of SiH2, SiHD, and SiD2 were studied to investigate excited-state dynamics and effects of the initial vibrational state. The cross section (sigma) for the photodissociation relative to SiH2(B)-->Si(1D)+H2 and the rovibrational population of the H2 fragment were computed using the wave packet propagation technique based on the three-dimensional potential energy surfaces (PESs) of the A and B electronic states and the transition dipole surfaces, which were reported in our previous paper [J. Chem. Phys. 122, 144307 (2005)]. The photodissociation spectrum consists of a broadband and a number of sharp peaks. For SiH2 and SiD2, the sharp peaks correspond to the resonance structure of the vibrational levels of the B state and the broadbands are nearly independent of the photon energy. The broadband for SiHD increases steeply with the photon energy above 30,000 cm(-1). The flux leaving the computational grid for SiH2 and SiD2 consists of at least two components, whereas that for SiHD consists of only a faster component. These large isotope effects were discussed based on the valley to the dissociation channel on PES and the difference in the position of the initial wave packet for three isotopomers.

Vibrational energies for the X1A1, A1B1, and B1A1 states of SiH2/SiD2 and related transition probabilities based on global potential energy surfaces.

Transition probabilities were evaluated for the X(1)A(1)-A(1)B(1) and A(1)B(1)-B(1)A(1) systems of SiH(2) and SiD(2) to analyze the X-->A-->B photoexcitation. The Franck-Condon factors (FCFs) and Einstein's B coefficients were computed by quantum vibrational calculations using the three-dimensional potential energy surfaces (PESs) of the SiH(2)(X(1)A(1),A(1)B(1),B(1)A(1)) electronic states and the electronic transition moments for the X-A, X-B, and A-B system. The global PESs were determined by the multireference configuration interaction calculations with the Davidson correction and the interpolant moving least-squares method combined with the Shepard interpolation. The obtained FCFs for the X-A and A-B systems exhibit that the bending mode is strongly enhanced in the excitation since the equilibrium bond angle greatly varies with the three states; the barrier to linearity is evaluated to be 21,900 cm(-1) for the X state, 6400 cm(-1) for the A state, and 230-240 cm(-1) for the B state. The theoretical lifetimes for the pure bending levels of the A and B states were calculated from the fluorescence decay rates for the A-X, B-A, and B-X emissions.