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Collisional deactivation of OH(X(super 2)pi,v=1-4) by N(H)3 was studied with pulsed laser probe technique. The deactivation of OH(v lesser than or equal to 3) by N(H)3 can be elucidated by nonresonant U-V energy transfer caused by long-range interaction.

Vibrationally excited formyl radicals (HCO), generated by the photolysis of acetaldehyde at 248 nm were examined using laser-induced fluorescence, a particular system was first used for the kinetic study of HCO. The highly directivity of the B(super 2) A' LIF made it possible to perform experiments at low initial concentrations, thereby suppressing undesirable second-order side reactions.

The overall rate constants for the collisions or vibrationally-excited OH(X2-Pi-(sub i), nu = 1-4) with CH4 were determined. The absolute rate constants for the reactive and nonreactive removal of OH(nu) were obtained by linear regression method and the previously determined nascent vibrational distribution of OH. The results showed that even a single quantum excitation of the OH vibration hastens the reactive removal of OH by CH4.

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 32S16O 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. [ABSTRACT FROM AUTHOR]

Excitation transfers between linear AlNC and AlCN via the à 1Π (1 1A″, 2 1A′)-X 1Σ+ 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 1A′-X 1Σ+ 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 1A″-X 1Σ+ 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 1Π-X 1Σ+ fluorescence of AlNC and AlCN, with even the initial wave packet being made with the vibrational ground level of the à 1Π 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. [ABSTRACT FROM AUTHOR]

The C 1B2-X 1A1 photoexcitation of SO2 was studied to investigate excited-state dynamics and the effects of the initial vibrational state. Ultraviolet photoabsorption cross sections (σ's) of seven isotopologues (32S 16O2, 33S 16O2, 34S 16O2, 36S 16O2, 32S16O17O, 32S16O18O, 34S16O18O) 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 σ’s of the seven isotopologues at 298 K; we concluded that the absorption spectrum of SO2 can be reliably modeled within the adiabatic framework based on the analysis of the time evolution of the wave packet. The calculated σ’s are in reasonable agreement with the recent experiment in the 190–228 nm region, and the isotope shifts of the peaks for 33S 16O2 and 34S 16O2 relative to the corresponding peaks for 32S 16O2 are in good agreement with the observed data. Relative to the σ of 32S 16O2, isotopic substitution shows a significant increment for those of 34S 16O2 and 36S 16O2 in the 190–228 nm region. This trend is consistent with the observed data. [ABSTRACT FROM AUTHOR]

Transition probabilities were evaluated for the X 1A1-à 1B1 and à 1B1-B 1A1 systems of GeH2 and GeD2 to analyze the X→Ã→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 1A1, à 1B1, and B 1A1 electronic states and the transition dipole moments for the X-à and Ã-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 à state, and 560 cm-1 for the B state. The obtained FCFs for the X-à and Ã-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-à system agree well with the observed spectra. The theoretical lifetimes for lower vibrational levels of the à and B states were calculated from the fluorescence decay rates for the Ã-X, B-Ã, and B-X emissions, and the lifetimes for the à state are in good agreement with the observed values except those affected by predissociation. [ABSTRACT FROM AUTHOR]

Transition probabilities were evaluated for the X 1Σ+-à 1Π system of AlNC and AlCN isomers to analyze photoabsorption and fluorescence spectra. The global potential energy surfaces (PESs) of the X 1Σ+ and à 1Π (1 1A″,2 1A′) 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 1A″ and X-2 1A′ 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 1A″ and X-2 1A′ systems are discussed comparing with the observed photoexcitation and fluorescence spectra. The lifetimes for the several vibrational levels of the à 1Π state were calculated to be ca. 7 ns for AlNC and 21–24 ns for AlCN from the fluorescence decay rates of the 1 1A″-X and 2 1A′-X emissions. [ABSTRACT FROM AUTHOR]

Dissociations after the à 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 (σ) 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 à 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. [ABSTRACT FROM AUTHOR]

Transition probabilities were evaluated for the X 1A1-à 1B1 and à 1B1-B 1A1 systems of SiH2 and SiD2 to analyze the X→Ã→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 SiH2(X1A1,Ã1B1,B1A1) electronic states and the electronic transition moments for the X-Ã, X-B, and Ã-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-à and Ã-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 à state, and 230–240 cm-1 for the B state. The theoretical lifetimes for the pure bending levels of the à and B states were calculated from the fluorescence decay rates for the Ã-X, B-Ã, and B-X emissions. [ABSTRACT FROM AUTHOR]

In order to elucidate the ionization dynamics, in particular the vibrational distribution, of H[sub 2]S[sup +](Ã) produced by the Penning ionization of H[sub 2]S with He[sup *](2 [sup 3]S) atoms, the Franck–Condon factors (FCFs) were presented for the H[sub 2]S(X)→H[sub 2]S[sup +](X,Ã) ionization and the H[sub 2]S[sup +](ÖX) transition, and Einstein’s A coefficients were presented for the latter transition. The FCFs were obtained by quantum vibrational calculations using the global potential energy surfaces (PESs) of H[sub 2]S(X [sup 1]A[sub 1]) and H[sub 2]S[sup +](X [sup 2]B[sub 1],à [sup 2]A[sub 1],B [sup 2]B[sub 2]) electronic states. 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 exhibit that the H[sub 2]S[sup +](X) state primarily populates the vibrational ground state since its equilibrium geometry is almost equal to that of H[sub 2]S(X), while the bending mode (ν[sub 2]) is strongly enhanced for the H[sub 2]S[sup +](Ã) state; the maximum in the population is around ν[sub 2]=6–7. In the same manner, the bending progressions are expected to consist of the great part of the H[sub 2]S[sup +](ÖX) emission. A detailed comparison with the experimental study for this system is reported in the accompanying paper, Paper II. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Emissions in the 200–750 nm region produced by the collision of He[sup *](2 [sup 3]S) with H[sub 2]S were studied under single-collision conditions. The hydrogen Balmer lines and the SH[sup +](A [sup 3]Π–X [sup 3]Σ[sup -]) and H[sub 2]S[sup +](à [sup 2]A[sub 1]–X [sup 2]B[sub 1]) bands were assigned. The total emission cross section (σ[sub em]) was evaluated to be (1.7±0.3)×10[sup -20] m[sup 2] at a collision energy of 150 meV. The σ[sub em]s of the SH[sup +](A–X) and H[sub 2]S[sup +](ÖX) bands decreased with increase in the collision energy in the 115–200 meV range, indicating that attractive forces are effective for the incident channels with regard to the formation of these species. The rotational distribution of SH[sup +](A [sup 3]Π,ν[sup ′]=0) is represented by a Boltzmann temperature of 870±80 K. The H[sub 2]S[sup +](à [sup 2]A[sub 1]–X [sup 2]B[sub 1]) emission, which was assigned for the first time in the Penning ionization of H[sub 2]S, primarily consists of the bending progressions. The internal populations of H[sub 2]S[sup +](Ã) were analyzed using the vibrational energies and Einstein’s A coefficients calculated in this study. The details of the calculation and derived spectroscopic constants are reported in the accompanying paper, Paper I. The populations obtained for the bending vibration (ν[sub 2][sup ′]) of H[sub 2]S[sup +](Ã) show an inverted distribution with a peak at ν[sub 2][sup ′]=3. This distribution is shifted lower compared that with a peak at ν[sub 2][sup ′]=4–5 observed by He[sup *](2 [sup 3]S) Penning ionization electron spectroscopy and that with a peak at ν[sub 2][sup ′]=6–7 predicted by the theoretical Franck–Condon factors for the H[sub 2]S(X)–H[sub 2]S[sup +](Ã) ionization. The origin of the difference is discussed concerning the formation mechanism of H[sub 2]S[sup +](à [sup 2]A[sub 1]). © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Several experiments are conducted to examine the quenching and vibratonal relaxation of f SO([B.sup.3][SIGMA.sup.-],[nu]' less than equal to 3) by preparing time-resolved fluorescence profiles at various buffer gas, namely Ar and [N.sub.2] pressures. The results show that the efficiency of quenching highly depends on the vibrational levels, as it is associated with the energies of the lowest nonfluorescent rotational levels.

Rate constants for vibrational relaxation of SO(B3sigma-, v' = 1 and 2) by collisions with He is determined. The branching ratios between quenching and vibrational relaxation of SO(A3II and B3sigma-) by monotomic gases are strongly dependent on the number of perturbed rotational levels.

Collision-free lifetimes and deactivation rate constants of SO(B(super 3)sigma(super -), v' =0,1, and 2) by collisions with He was determined. SO(X(super 3)sigma(super -)) was generated in the photolysis of SO2 at 193 nm (ArF laser) and excited to a single rovibrational level of B(super 3)sigma(super -) with a pulsed ultraviolet laser.

Emission spectra in the 190–600 nm region produced by electron impact on BCl3 have been studied up to 110 eV. Emission cross sections of the B(2s2p2 2D–2p 2P0) and B(3s 2S–2p 2P0) lines and the BCl(A 1Π–X 1Σ+) band are evaluated to be 4.9±1.0, 4.5±0.7, and (1.9±0.3)×10-18 cm2, respectively, at 100 eV. Formation cross sections of these species have been determined from the analysis of their fluorescence decaying curves. Two continuous emissions observed in the 230–380 and 400–580 nm regions are attributed to the BCl[ATOTHER]@B|[/ATOTHER]2 band. The fluorescence lifetime of BCl*2 in the 300–342 nm region is obtained to be 1.65±0.2 μs, which is nearly independent of the wavelength. [ABSTRACT FROM AUTHOR]

Fluorescence spectra of the N2O+(A 2Σ+–X 2Πi) system produced by electron impact on N2O have been studied in the impact energy range of 22–100 eV in order to determine vibrational-state distributions of the N2O+(A 2Σ+) state. Emission bands from the 00, 21K1, 22K0, 11, 12, and 31 levels have been assigned. The populations of the 11 and 12 levels corrected for effects of predissociation are similar to those obtained by the threshold photoelectron method. It is concluded that these results are affected by autoionization via the Rydberg states converging to the C 2Σ+ ion state. The population of the 21K1 level is enhanced remarkably more than in photoionization data. This enhancement indicates that, in the electron impact, transitions with ΔK=±1 are allowed in the formation of A 2Σ+. [ABSTRACT FROM AUTHOR]

Fluorescence spectra of the A2Πu–X2Πg system of CO+2 and CS+2 ions, following electron impact on supersonic jet targets of CO2 and CS2, have been analyzed to determine vibrational populations. The vibrational distributions of the A2Πu state of CO+2 and CS+2 were found to be independent of the impact energy in the 30–300 eV range. The distribution of the CO+2(A) state is very similar to the result obtained by He i photoelectron spectroscopy (PES), which is a Franck–Condon-type vertical ionization, whereas that of the CS+2(A) state is significantly different from the PES data. This non-Franck–Condon behavior for formation of CS+2(A) in the electron impact is discussed. [ABSTRACT FROM AUTHOR]

Photoabsorption cross sections of thiirane and thietane vapors have been studied in the 110–240 nm region using synchrotron radiation. A number of peaks from thiirane and thietane are arranged into four and five Rydberg series, respectively, converging to the first ionization potential. Many Rydberg peaks from both molecules are observed to possess vibronic structures. The vibrational progressions from thiirane are assigned to the CH2 wagging (ν4) and CS symmetry stretching (ν5) modes. For thietane, the CH2 wagging (ν5) and CS symmetry stretching (ν7) modes of the excited states are found to be active. Molecular geometries and vibrational frequencies for the excited states are discussed on the basis of ab initio calculations. [ABSTRACT FROM AUTHOR]

Analyzes the photoemission cross sections for the A-X, B-X and C-X bands of the CH radical produced by collisions of He(2(supra 3)S) atoms with CH(sub 3) (X=H, Cl, Br, I). Good correlation found between the sum of the photoemission cross section values for CH and the dipole induced interaction of He(2(supra 3)S) with targets; Positive energy dependemce for methane.

The application of a kinetic method to ascertain the nascent vibrational phase populations of NH2(X(super ~)(super 2)B1) obtained in the 193 nm photolysis of NH3 is described. The kinetic analysis determines relevant identifications of vibrational levels from noted time profiles.

The mechanism for the Penning ionization based on the internal distributions of the product ions and the potential surfaces calculated for both the entrance and exit channels. He (2(super 3) S) Penning ionization of HC1 and HBr leading to HC1 (super+) (A) and HBr (super+) (A) are studied optically by using a crossed-beam apparatus.