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Global potential energy surfaces (PESs) of SiCN/SiNC in the X ˜ 2 Π (A′ and A″) electronic state have been determined from MRCISD/aug-cc-pVTZ computations. Although spin–orbit coupling with lower-lying quartet states has a maximum of 3.4 cm −1 near linear SiCN, it is found to be negligible for bending form. Vibrational energies with J = 0 and 1 were computed up to 360 levels by quantum vibrational calculations using the three-dimensional PESs of the lowest 2 A′ and 2 A″ states. The Renner parameters for the linear SiCN and SiNC estimated from the lowest bending level are 0.300 and 0.283, respectively.

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.

Fluorescence from a single vibronic level of SO(B3Sigma-, v'or= 3) prepared by a pulse excitation has been detected and thorough kinetic analyses for the photochemical processes have been made. Deconvolution analysis by the integrated-profiles method of the time-resolved fluorescence profiles recorded at various buffer gas (Ar and N2) pressures has given the deactivation rates of initially prepared vibrational levels. Componential analysis of the dispersed fluorescence measured at different buffer gas pressures has provided the rate coefficients for level-to-level vibrational relaxation. It has been found that not only the single-quantum relaxation (Deltav = 1) but also the multiquantum relaxation (Deltav = 2 and 3) occurs by collisions with Ar and N2. The efficiency of quenching is strongly dependent on the vibrational levels and correlates with the energies of the lowest nonfluorescent rotational levels. Candidates for the electronic states governing the quenching process have been discussed based on the kinetic and spectroscopic data.

The time profiles of fluorescence from a single vibrational level of SO(B 3 Σ − , v ′ = 3) were recorded at various He pressures. The radiative lifetime, 29 ± 4 ns determined by a deconvolution analysis, is nearly identical with those of v ′ v = 1, and multiquantum relaxation Δ v = 2 and 3, have been obtained from the He pressure dependence of dispersed fluorescence spectra. The Franck–Condon factors for v ′ = 3 → v ″ = 0–23 in the B 3 Σ − –X 3 Σ − system have also been determined.

To elucidate the ionization dynamics, in particular the vibrational distribution, of H 2 O +(Ã) produced by photoionization and the Penning ionization of H 2 O and D 2 O with He *(2 3S) atoms, Franck–Condon factors (FCFs) were given for the [Formula: see text] ionization, and the transition probabilities were presented for the [Formula: see text] emission. The FCFs were obtained by quantum vibrational calculations using the three-dimensional potential energy surfaces (PESs) of [Formula: see text] and [Formula: see text] electronic states. The global PESs were determined by the multi-reference 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 [Formula: see text] state primarily populates the vibrational ground state, as its equilibrium geometry is almost equal to that of [Formula: see text], while the bending mode (ν2) is strongly enhanced for the H 2 O +(Ã) state; the maximums in the population of H 2 O + and D 2 O + are approximately v2 = 11–12 and 15–17, respectively. These results are consistent with the distributions observed by photoelectron spectroscopy. Transition probabilities for the [Formula: see text] system of H 2 O + and D 2 O + show that the bending progressions consist primarily of the [Formula: see text] emission, with combination bands from the (1, v′2 = 4–8, 0) level being next most important.

Rate coefficients for deactivation of SO(X 3 Σ - , v = 1-5) by collisions with SO 2 and nascent vibrational populations in v = 0-2 in the photolysis of SO 2 at 193.3 nm have been determined. A single vibrational level of SO(X 3 Σ - ) was detected with laser-induced fluorescence (LIF) excited via the B 3 Σ - -X 3 Σ - system. Time-dependent profiles of LIF signals were recorded as a function of the pressures of SO 2 . Observed profiles were analyzed by the integrated-profiles method and reproduced well by convolution calculations. Overall rate coefficients for vibrational relaxation of SO(v) by SO 2 have been determined to be (4.7 ′ 0.5) × 10 - 1 2 (v = 1), (6.7 ′ 0.4) x 10 - 1 2 (v = 2), (7.2 ′ 0.7) x 10 - 1 2 (v = 3), (6.1 ′ 1.0) x 10 - 1 2 (v = 4), and (8.6 ′ 0.7) × 10 - 1 2 (v = 5) in units of cm 3 molecule - 1 s - 1 (the quoted errors are 2σ). We have also found that 63% of the vibrational deactivations of v = 2 by SO 2 are governed by double-quantum relaxation: (4.2 ′ 0.9) x 10 - 1 2 cm 3 molecule - 1 s - 1 for v = 2 → v = 0 and (2.5 ′ 0.9) x 10 - 1 2 cm 3 molecule - 1 s - 1 for v = 2 → v = 1. Ab initio calculations enable us to find two stable complexes: OS-OSO and SO-SO 2 , indicating that attractive interactions play a significant role in the relaxation. The nascent vibrational distributions of SO have been measured to be 0.52 ′ 0.1/0.75 ′ 0.1/1.0 for v = 0/½. The differences in vibrational distributions reported by bulk and beam experiments are attributed to the difference in the temperature of parent SO 2 .

Rate constants for vibrational relaxation of SO(B 3 Σ - , υ' = I and 2) by collisions with He have been determined. SO(X 3 Σ - ) was generated in the photolysis of SO 2 at 193 nm, and excited to a single vibrational level of the B 3 Σ - state with a tunable UV laser. Dispersed fluorescence spectra were recorded as a function of buffer gas pressures (He, 30-150 Torr). Observed spectra are composed of fluorescence from the initially excited level and those from levels populated by vibrational relaxation. Kinetic analyses of relative fluorescence intensities give rate constants for both single- and double- quantum vibrational relaxation: (7.7 ′ 1.0) x 10 - 1 3 for υ' = 1 → υ' = 0, (1.0 ′ 0.2) × 10 - 1 1 for υ' = 2 → υ' = 1, and (1.7 ′ 0.3) × 10 - 1 2 for υ' = 2 → υ' = 0, in units of cm 3 molecule - 1 s - 1 (the quoted errors are 2σ). It has been found that the branching ratios between quenching and vibrational relaxation of SO(A 3 Π and B 3 Σ - ) by monatomic gases are strongly dependent on the number of perturbed rotational levels.

Collision-free lifetimes and deactivation rate constants of SO(B3Σ-, v‘ = 0, 1, and 2) by collisions with He have been determined. SO(X3Σ-) was generated in the photolysis of SO2 at 193 nm (ArF laser) and excited to a single rovibrational level of B3Σ- with a pulsed ultraviolet laser. We recorded dispersed fluorescence spectra, and found that 0−12 (350.8 nm), 1−14 (368.5 nm), and 2−17 (401.2 nm) bands are suitable for detecting fluorescence from single vibrational level of interest. Time profiles of wavelength-resolved fluorescence were recorded at various buffer gas pressures (5−165 Torr of He). Deconvolution by the integrated phase plane method derives apparent fluorescence lifetime at a given pressure. Total pressure dependence of fluorescence decay rates leads to collision-free lifetimes and rate constants for deactivation of SO(B3Σ-, v‘ = 0, 1, and 2) by collisions with He. Lifetimes of SO(B3Σ-) have been determined to be (28 ± 2) ns (v‘ = 0), (30 ± 3) ns (v‘ = 1), and (27 ± 4) ns (v‘ = 2). Rate coef...

Nascent vibrational distributions of NH 2 (X 2 B 1 , υ 2 " = 0-4) generated in the 193 nm photolysis of NH 3 at 298 ′ 1 K have been determined by simple kinetic analysis. The vibrational levels of NH 2 (X 2 B 1 ) were detected by laser-induced fluorescence (LIF) excited via the A 2 A 1 -X 2 B 1 system, and time-resolved concentration profiles were recorded. Rate constants for intramode relaxation of ν 2 vibration (υ 2 " → υ 2 "-1) by collisions of He have been determined to be (4.2 ′ 1.0) × 10 - 1 4 , (7.5 ′ 0.5) × 10 - 1 4 , (1.6 ′ 0.1) × 10 - 1 3 , (3.0 ′ 0.1) × 10 - 1 3 in units of cm 3 molecule - 1 s - 1 for υ 2 " = 1, 2, 3, and 4, respectively. The quoted errors are 2σ. Rate constants for intermode coupling between υ 1 " = I and υ 2 " = 2 by He have also been determined to be (4.7 ′ 1.6) × 10 - 1 2 (υ 1 " =1 → υ 2 " = 2) and (1.3 ′ 0.4) × 10 - 1 2 cm 3 molecule - 1 s - 1 (υ 1 " =1 ← υ 2 " = 2). Relative detectivities of the levels υ 2 " = 1-4 were obtained by the kinetic analysis, and vibrational distributions immediately after the photolysis have been given to be 2.2 ′ 0.7/1.0/ < 1.3/0.66 ′ 0.3/ < 3.0 for υ 2 " = 0/½/3/4 (normalized by the population of υ 2 " = 1 ). To the best of our knowledge, this is the first quantitative report on the initial vibrational populations of NH 2 generated in the photolysis at 193 nm.

The rate constants for reactions NH2(X2B1, v2 = 0 and 1) + NO have been determined at 298 ± 1 K using the pulsed UV photolysis/pulsed laser-induced fluorescence (LIF) technique. NH3 was photolyzed with an ArF excimer laser (193 nm), and NH2(X2B1, v2 = 0 and 1) were detected by LIF in the A2A1−X2B1 system. It has been found that CF4 is efficient at vibrational relaxation of NH2, and the rate constant for deactivation of NH2(X2B1, v2 = 1) by CF4 has been determined to be [3.2 ± 0.5(2σ)] × 10-11 cm3 molecule-1 s-1. Fast vibrational relaxation of NH2 by CF4 prior to the reaction with NO permits us to obtain an accurate rate constant for NH2(X2B1, v2 = 0) + NO. The rate constant measured in N2 buffer gas at 1 Torr is [2.05 ± 0.1(2σ)] × 10-11 cm3 molecule-1 s-1. The sources of discrepancy in previously reported room-temperature rate constants have been discussed on the basis of a survey of the experimental conditions and the methods of analysis. The overall rate constant for NH2(X2B1, v2 = 1) + NO has bee...

The photoemissions from fragments produced by collisions of He(23S) atoms with CHCl3, CCl2F2, CCl3F, CCl4, and CBrCl3 have been studied in the collision energy range of 120–210 meV using a crossed beam. The Cl2(D′–A′) band is predominant for CCl4 and CBrCl3, while the A–X and B–X bands of CF are intense for CCl2F2 and CCl3F. The sum of the emission cross sections (σem) for several systems of neutral fragments in the 190–600 nm region was estimated to be in the (0.3–1.2) × 10−20 m2 range for these chloromethanes at a collision energy of 150 meV. The dependences of σem’s for the Cl2(D′–A′) band from CHCl3 and CCl4 on the collision energy are either nearly zero or slightly negative. The sum of σem’s for Cl2 and other ion-pair bands reveals a fairly good correlation with the electron affinity of the targets. These results support the harpoon mechanism for the formation of Cl2(D′) from the He(23S) + chloromethanes reactions.

Vibrationally excited formyl radicals (HCO) were generated by the photolysis of acetaldehyde at 248 nm and detected by using laser-induced fluorescence (LIF). LIF via the B2A‘−X2A‘ UV system was first used for the kinetic study of HCO. The high detectivity of the B2A‘−X2A‘ LIF made it possible to perform experiments at low initial HCO concentrations, thereby suppressing undesirable second-order side reactions. The rate constants for the total removal of three vibrational levels of HCO (X2A‘, ν1ν2ν3 = 000, 010, 001) by O2 have been determined to be [6.6 ± 0.3(2σ)] × 10-12, [8.7 ± 1.5(2σ)] × 10-12, and [6.3 ± 1.1(2σ)] × 10-12 cm3 molecule-1 s-1, respectively. This study is the first measurement of the rate constant for the HCO(001) + O2 reaction. An upper limit of the OH production yield was determined to be 3 × 10-3 on the basis of a calibration of LIF intensities of HCO and OH. A comparison with previous kinetic studies is made, and the causes of the differences are discussed.

Photoemissions from excited fragments and molecular ions produced by collisions of He(2 3S) with SiCl4 and GeCl4 have been studied at the relative collision energy of 120—210 meV. Total emission cross sections in the 200—760 nm range for SiCl4 and GeCl4 are evaluated to be 4.5 ± 0.8 and 2.2 ± 0.4, respectively, in 10−20 m2 units. Emission cross sections for SiCl4+(), GeCl4+(), and Ge I atomic lines slightly decrease with increases in the collision energy. This originates from the fact that the effective potentials of He(2 3S) with SiCl4 and GeCl4 are slightly attractive. The branching ratio of Ge I states observed from GeCl4 is consistent with a simple dissociation model assuming equipartition of the available energy. These results are compatible with the harpoon mechanism as an initial step for formation of Ge I from GeCl4. The emission cross section for the SiCl(B′–X) band increases with the collision energy. This indicates that the effective potential between He(2 3S) and SiCl4 is repulsive, and that t...

Absolute rate constants for reactive removal and vibrational relaxation have been determined for the collisions of OH({Chi}{sup 2}{Pi}{sub i}, {upsilon} = 1 and 2) with CH{sub 4}. The hydroxyl radical was produced in the reaction O({sup 1}D) + CH{sub 4} {r_arrow} OH({Chi}{sup 2}{Pi}{sub i}, {upsilon} {le} 4) + CH{sub 3} initiated by the 248 nm photolysis of O{sub 3} in the presence of CH{sub 4}. All the vibrational levels of OH({upsilon}) were detected by laser-induced fluorescence (LIF) via the sequences {Delta}{upsilon} = 0 ({upsilon}{double_prime} = 0, 1, and 2) and {Delta}{upsilon} = {minus}3 ({upsilon}{double_prime} = 3 and 4) of the {Alpha}{sup 2}{Sigma}{sup +}{minus}{Chi}{sup 2}{Pi}{sub i} transition. Temporal profiles of the LIF intensities were analyzed using a new linear regression method, and total removal rate constants for the vibrational levels ({upsilon} = 1--4) were determined. The linear analysis coupled with the previously reported nascent vibrational distributions of OH gave absolute rate constants for the reactive and nonreactive removal of OH({upsilon}). Rate constants for reactive removal, OH({upsilon}) + CH{sub 4} {r_arrow} products, were determined to be {kappa}({upsilon} = 1) = (2.1 {+-} 0.6) {times} 10{sup {minus}13} cm{sup 3} molecule{sup {minus}1} s{sup {minus}1} and {kappa}({upsilon}=2) = (0.9 {+-} 0.4) {times} 10{sup {minus}12} cm{supmore » 3} molecule{sup {minus}1} s{sup {minus}1}, and for vibrational relaxation, OH({upsilon}) + CH{sub 4} {r_arrow} OH({upsilon} {minus} 1) + CH{sub 4}, are {kappa}(1{r_arrow}0) = (3.5 {+-} 0.6) {times} 10{sup {minus}13} cm{sup 3} molecule{sup {minus}1} s{sup {minus}1} and {kappa}(2{r_arrow}1) = (1.1 {+-} 0.4) {times} 10{sup {minus}12} cm{sup 3} molecule{sup {minus}1} s{sup {minus}1}. This article is the first report on the branching ratios between reactive removal and vibrational relaxation.« less

A new apparatus has been constructed to eliminate the self-absorption effect from dispersed emission spectra. Droplets of solution smaller than 5 μm in diameter were generated by ultrasonic vibration from bulk solution, and irradiated with a laser to observe dispersed emission spectra. Effective suppression of self-absorption was demonstrated using ethanol droplets containing rhodamine 640 dye. A slight increase in the ambient temperature—less than 10°—gave rise to a release of solvent molecules from droplets, and consequently, the size of the droplets drastically decreased. Emission spectra over a wide range of concentrations were observed by the method of solvent release. The change of the ratio between monomer/excimer fluorescence from pyrene was clearly shown using droplets generated from solution with single concentration. Effective concentrations and the sizes of droplets at different temperatures were determined from comparison to the results obtained by droplets with different concentrations. The concentration of droplets warmed up to 305 K and was 29 times that of droplets at 297 K.

Photoabsorption and fluorescence cross sections of SnCl 4 and Sn(CH 3 ) 4 have been measured in the 6–31 eV region by using synchrotron radiation. Bands above 8 eV observed in the photoabsorption and fluorescence excitation spectra of SnCl 4 have been assigned as the ( n p, 4d) ← 1t 1 , (4s, n p, 4d) ← 3t 2 , n p ← 1e and (4s, 4p) ← 2t 2 Rydberg transitions where n = 4−6, whereas the bands observed from Sn(CH 3 ) 4 were too broad to assign. For SnCl 4 , strong emissions produced by 10.9 eV radiation have been assigned to the A 1 B 1 -X 1 A 1 and 3 B 1 -X 1 A 1 transitions of the SnCl 2 radical, while several Sn I lines were observed by 21.5 eV radiation. In the fluorescence excitation spectrum of Sn(CH 3 ) 4 , a band attributable to Sn I lines was observed in the 18–23 eV region.

Rotational-state distributions of the CO + (A–X, B–X) and N 2 + (B–X) emissions produced by the collisions of He(2 3 S) with CO and N 2 were studied in the collision energy ( E R range 100–200 meV. The rotational populations of the emitting states can be fitte by single Boltzmann temperatures ( T R . The T R (320 ± 30 K) for the ν ′ = 3 and 4 levels of the CO + (A 2 Π) state are nearly independent of, or slightly increase with, E R , while T R for the CO + (B 2 Σ + , ν ′ = 0) state increases rapidly with E R .The T R (430 ± 20 K) for the N 2 + (B 2 Σ + , ν ′ = 0) state is nearly independent or slightly decreases with increasing E R . Interactions providing these trends are discussed.

Photoemissions at 200—650 nm resulting from the He(23S) Penning ionization of CO2, CS2, OCS, N2O, C6F6, and C6F5H have been studied in the collision energy range of 120—210 meV using a crossed-beam method. The emission cross sections obtained for the excited parent ions were compared with the values measured at thermal energy. The band strengths for the vibrational bands of the OCS+() system are rather different from the values measured by the photoionization of OCS. The dependences of the emission cross sections for triatomic ions on the collision energy have been compared with those of the partial cross sections for the ion states obtained by Penning ionization electron spectroscopy, and the interaction potentials between He(23S) and the triatomic molecules correlating with the Penning ionization are discussed.

Fluorescence in the 200—600 nm range from excited fragments produced by collision of He(23S) with SnCl4 and Sn(CH3)4 has been studied in the relative collision energy of 135—210 meV. Emission cross sections for Sn I atomic resonance lines from SnCl4 slightly decrease with increasing collision energy. This originates from the fact that the effective potential between He(23S) and SnCl4 is slightly attractive. The branching ratio of Sn I states observed from SnCl4 is consistent with a simple dissociation model assuming equipartition of the available energy. These results are compatible with the harpoon mechanism as an initial step for formation of Sn I from SnCl4. On the other hand, the effective potential between He(23S) and Sn(CH3)4 is found to be repulsive, and the branching ratio of Sn I is increased to much more than that estimated from the statistical model. Excited Sn I states seem to be produced directly from Sn(CH3)4 by an excitation transfer mechanism via superexcited states, which mainly decay by ...

The overall rate constant for the reaction NH(a1Δ ) + HN3 has been determined by the laser photolysis of hydrogen azide (HN3) at 266 nm and 193nm. The visible emission from vibronically excited NH2(A˜2A1) was dispersed and its time-dependent profiles were measured at several wavelengths. The rate constants are dependent not only on the photolysis wavelengths but also on the vibrational levels of the NH2(A˜2A1) produced in the reaction. The intermolecular potential between NH(a1Δ) and HN3 was determined to be the form V(R) = –C/Rs (2 < s < 4, C: constant) from the analysis with a long-range potential approximation. The interaction between NH(a1Δ ) and HN3 is mainly governed by the dipoledipole interaction in the initial stage of the reaction.

The CS(A 1 Π-X 1 Σ + ) emission spectra produced by electron impact on CS 2 and OCS have been measured from threshold up to 120 eV. Emission cross sections of this band from CS 2 and OCS are 10±2 and (0.75±0.15) ×10 -18 cm 2 , respectively, at 100 eV. At low impact energies (below 20 eV), the vibrational state distributions of CS(A 1 Π, ν'=0-8) measured from CS 2 and OCS can be represented by temperatures of 12 500±2000 and 26 000±4000 K, respectively, while the rotational temperature of the ν'=0 level is estimated to be 3850± 400 K from both parents

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.

The excitation-transfer reaction between N 2 (A 3 Σ u + ) and CF 2 (X 1 A 1 ) has been studied in a discharge-flow reactor. Dispersed emission spectra show that the spin-forbidden excitation CF 2 (a 3 B 1 ← X 1 A 1 ) is favored over the spin-allowed transition CF 2 (A 1 B 1 ← X 1 A 1 ). The selectivity is discussed in terms of conservation of total electronic spin and energy defect in the transfer process. The present observation is the first successful excitation of a carbene by energy-transfer from N 2 (A 3 Σ + u ). Several reasons for the previous lack of success (Cao and Setser) are found from careful comparison of the concentrations of reagents and power of the discharge.

The CCl(A 2Δ-X 2Π) emission at 278 nm produced by electron impact on CCl4 and related molecules have been studied up to 110 eV. Photoemission cross sections of the CCl(A-X) system from CHCl3, CFCl3, CCl4 and CBrCl3 are evaluated to be 1.87 ± 0.27, 3.38 ± 0.45, 8.6 ± 1.3 and (7.5 ± 1.0) × 10−19 cm2, respectively, at 100 eV. The rotational temperature of the CCl(A 2Δ, v′=0) state produced by electron impact on CCl4, 3000 K, is found to be very much higher than the temperature (600 K) of that excited in microwave discharge of CCl4/Ar mixtures. This result indicates that in CCl4 discharges CCl(A) is not produced directly by electron-impact dissociation of CCl4 at low CCl4 molar fractions.

The chemiluminiscent reaction following the ultraviolet (266 nm) photolysis of HN 3 has been studied. A dispersed emission spectrum was recorded, which is, to the best of our knowledge, the first direct identification of the origin of the chemiluminescence. The emissive species was assigned to vibronically excited NH 2 . The observed vibrational distribution in the NH 2 (A 2 A 1 ) was not consistent with the reaction mechanism previously suggested (NH(a 1 Δ, v = 0) + HN 3 ). A modified mechanism including vibrationally excited NH(a 1 Δ) has been proposed on the basis of energetics and kinetics in terms of the emission.

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.

Photoemission cross sections of Penning ionization have been measured at 150 meV for collision of He*(2 3S) with N2O by using the crossed-beam method and observing fluorescence in the 335–415 nm region. The emission cross section of the N2O+ (A2Σ+ −X 2Π) system obtained is (7.7 ± 2.1) × 10−20 m2. The band strengths of the 110 and 311 bands relative to the 000 band, s(110)/s(000) and s(311)/s(000, are evaluated to be 0.105 ± 0.007 and 0.045 ± 0.003, respectively. The s(110)/s(000) ratio indicates non-Franck-Condon behavior, which is attributable to the 7δ→eδ shape resonant ionization near 20 eV.

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+.

Fluorescence spectra of the A-X system from parent ions produced by electron impact on N2O, CO2 and CS2 in supersonic jets have been measured in the 30–300 eV range to study the details of rotational excitation. The rotational state distributions of the product ions are essentially Boltzmann and the effective rotational temperatures increase with decreasing impact energy to the threshold. The net increase in the rotational energy from 300 to 30 eV is 0.9 meV for N2O+(A), 0.9 meV for CO+2(A) and 1.7 meV for CS+2(A). This trend of rotational excitation is mainly ascribed to angular momentum transfer through the quadrupole interaction between the scattered and ejected electrons and the produced ion.

Emission spectra of the N2O+ (A 2Σ+−X2Πi) system produced by electron impact on jet-cooled N2O have been measured at impact energies of 18–300 eV. The vibrational population for the 11 level relative to the 00 level of the A state was found to decrease rapidly with increasing impact energy and level-off above 30 eV, whereas that for the 31 level was essentially constant. The branching ratio, σ(11)/σ(00), at higher impact energies deviates from what can be expected from vertical ionization based on the Franck—Condon principle. This non-Franck—Condon behavior is probably caused by autoionization of the Rydberg states converging to the C 2Σ+ ion state.

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.

Emission spectra in the 180–600 nm region produced by electron impact on CHCl3, CFCl3, CCl4 and CBrCl3 have been studied. A broad band at 258 nm observed from all compounds is assigned to the D′ 2g-A′ 3Πu transition of Cl2, which is found to be produced by single collisions of parent molecules with electrons. Continuous emissions in the 420–580 nm region from CCl4 and CBrCl3 are assigned to the CCl2(A 1B1-X 1A1) transition. Radiative lifetimes of several fragments are obtained. Dissociation processes leading to electronically excited fragments are discussed.

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.

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.

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.

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.

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.

The rotational structures of the (0,0) sequence of the violet (B 2 Σ-X 2 Σ) band system of CN produced by the electron-impact dissociative excitation of HCN were measured under such conditions that secondary reactions can be disregarded. The distribution of the spectral intensity was essentially independent of the electron energy (80–300 eV). The rotational energy distributions of the ν′ = 0, 11, 12 and 13 levels of the B 2 Σ state can be approximated by two Boltzmann functions; the intensities for higher K fit the distribution for effective temperatures of 1080–1500 K, and those for lower K for 300–380 K. The formation mechanisms of the CN(B 2 Σ) are discussed.

The (0,0) sequence of the violet (B 2 ΣX 2 Σ) band system of CN produced by the electron impact dissociative excitation (200 eV) of HCN, BrCN and C 2 N 2 was measured. From the relative intensities of the R(14) lines split by rotational perturbation, the ratio of the formation rate of the A 2 Π state to that of the B 2 Σ state was estimated to be about 0.9, 1.9 and 0.8 for the CN radicals produced from HCN, BrCN and C 2 N 2 , respectively. These values are about 1/5 of the corresponding ratios observed by Coxon et al. for the impact of argon metastable atoms ( 3 P 0,2 ) on HCN and BrCN.

In the wavelength region of 200–600 nm, photoemissions from electronically excited H, CH, C2, and CS (only from thiophene and tetrahydrothiophene) were observed when furan, tetrahydrofuran, thiophene, and tetrahydrothiophene were excited by electron impact (0–70 eV). Hydrogen atoms (n=4) and CH(A2Δ) radicals were produced from these five-membered heterocycles via single collision excitations, while CS(A1Π) radicals from thiophene and tetrahydrothiophene were partly formed in secondary processes. The appearance potentials for the hydrogen Balmer β and the CH(A2Δ-X2Π) bands from these five-membered heterocycles are determined, and the dissociation processes forming H(n=4) and CH(A) are discussed.

Photoabsorption cross sections and fluorescence excitation spectra of dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) vapors have been studied in the 110–220 nm region using synchrotron radiation. For DMS, a new Rydberg series originating from the ns orbital is identified. A number of broad bands from DMDS are assigned as Rydberg transitions. Emissions from DMS and DMDS are assigned as the CH3( A - X ) band. For DMDS, another emission which is attributable to the S2(B-X) band appears in the excitation below 125 nm. Photodissociation processes forming the excited fragments are discussed.

Emission spectra in the 190–600 nm region produced by electron impact on CBr4, CHBr3 and CFBr3 have been studied. The continuous emissions in the 220–340 nm region found in all compounds are assigned to transitions from the D′ 2g, E 0g+ and D 0u+ ion-pair states of Br2. Radiative lifetimes of the D′ and D states of Br2 are obtained to be 26±3 and 28± 3 ns, respectively.The onsets for the Br2 emissions have been determined and dissociative excitation processes leading to excited diatomic fragments are discussed.

Emission spectra of the NH(A 3Π1−X3Σ) and NH(c 1Π−a 1Δ) systems are observed by the electron impact of ammonia from the threshold energies up to 120 eV. The formation of NH(A) and NH(c) by the dissociative excitation of ammonia was investigated. The ratio of the vibrational populations, P(v′ = 1)/P(v′ = 0) for NH(A 3Π) is 0.4–0.6, depending on the impact energy. The rotational energy distribution of the v′ = 0 level of the c 1Π state can be approximated by the effective Boltzmann temperature of 1690 ± 100 K. The rotational excitations of the v′ = 0 and v′ = 1 levels of the A3Π state are much higher and their rotational populations deviate from Boltzmann distributions, showing slight dependence on the impact energy. The ratio of the formation rate of NH(A) to that of NH(c) is estimated from the threshold to 92 eV.

Internal energy distributions of NH(A) produced by electron impact on NH3, HN3, and HNCO are compared with those predicted by use of the phase space theory based on the method of Light and Pechukas. The values predicted under conservation of energy and total angular momentum are found to be inconsistent with the experimental results. The observed values are well simulated via the introduction of a nonstatistical bias by representing the selective coupling between the reaction coordinate and the rotational modes of the products. The dynamics for formation of NH(A) is discussed.

Benzene, pyridine, and pyrazine were excited by electron impact (0–70 eV) under low pressure conditions. In the wavelength region of 250–510 nm, emissions from H, CH, C2, and CN (except for benzene) fragments were observed. Formations of H(n=4) and CH(A2Δ) from benzene, pyridine, and pyrazine were investigated. The appearance potentials for the hydrogen Balmer β emission were determined to be 19.5±1.0 eV in benzene, 19.7±1.0 eV in pyridine, and 19.6±1.0 eV in pyrazine. The appearance potentials for the CH(A-X) emission were also determined to be 12.7±1.0 and 21.4±1.0 eV in benzene, 20.1±1.0 eV in pyridine, and 18.5±1.0 eV in pyrazine. No emissions from the excited parent species of pyridine and pyrazine were observed.

Emission spectra of the NH(A 3 Π-X 3 Σ − ), NH(c 1 Π-a 1 Δ), NCO(A 2 Σ + -X 2 Π) and NCO(B 2 Π-X 2 Π) systems were observed by electron impact on HNCO up to 40 eV. The NH(c 1 Π) is shown to be formed directly, with the onset of 9.1 ± 0.6 eV. The onsets of NCO(A 2 Σ + ) and NCO(B 2 Π) formation are found to be 8.3 ± 0.6 and 9.2 ± 0.6 eV, respectively. The observed internal energy distributions for NH are compared with those predicted statistically. The precursor states forming NH(A), NH(c), NCO(A) and NCO(B) are discussed with the aid of a schematic correlation diagram based on a semi-empirical calculation (CNDO/S).

Etude des spectres d'emission de NH(A 3 Π-X 3 Σ − ) et NH(c 1 Π-a 1 D), formes par impact electronique (jusqu'a 50 eV) sur N 2 H 4 ou CH 3 NH 2 . Rapport de formation de ces etats c/A. Interpretation des distributions d'energie interne par un modele statistique simple