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The absorption spectra of acetylene molecules was measured under jet-cooled conditions in the wavelength range of 142.8152.3 nm, with a tunable and highly resolved vacuum ultraviolet (VUV) laser generated by two-photon resonant four wave difference frequency mixing processes. Due to the sufficient vibrational and rotational cooling effect of the molecular beam and the higher resolution VUV laser, the observed absorption spectra exhibit more distinct spectral features than the previous works measured at room temperature. The major three vibrational bands are assigned as a C-C symmetry stretching vibrational progress (u2 = 02) of the C1 IIu state of acetylene. The observed shoulder peak at 148.2 nm is assigned to the first overtone band of the trans-bending mode u4 of the C1 IIustate of acetylene. Additionally, the two components, 4o2(1IIu) and 4o2(1 IIuare suggested to exhibit in the present absorption spectra, due to their RennerTeller effect and transition selection rule. All band origins and bandwidths ...

Collisional removal of the (0,00,0) level of the A 2 Σ + state of the NCO radical has been studied at room temperature (298 K). NCO radicals were produced by laser photolysis of CHBr3 at 266 nm followed by the reaction of CH with N2O, then electronically excited with Nd:YAG laser pumped dye laser. The quenching rate coefficients kq and thermally averaged cross-sections σq were determined by the pressure dependence of the time-resolved fluorescence. Colliders investigated are Ar, N2, O2, CO, NO, N2O, CO2, SO2, H2O and photochemical precursor CHBr3. The quenching rates increase on the whole with the increasing of polarities of the colliders. By comparison with the formation cross-sections of complexes calculated by means of a collision complex model, it is believed that the attractive forces play main roles in the collision quenching processes of NCO ( A 2 Σ + ) by the quenchers studied in this work.

The probable reaction mechanism for the reaction of excited nitrogen atom and chloromethane has been studied using the G2MP2 method. Based on the calculated reaction processes, the excited nitrogen atom will insert into the CCl bond firstly to form the intermediate trans -CH 3 NCl, which can subsequently decompose and isomerize to further products. The present result suggests that CH 2 NCl is the most feasible among all possible products. The reaction mechanisms for the N ( 2 D )+ CH 3 X (X=H, F, Cl) system are contrasted in detail.

The [1+1] A 2Πu-state resonance enhanced two-photon dissociation process of CS2+ molecular ions has been investigated by measuring the photofragment S+ excitation (PHOFEX) spectrum in the wavelength range of 424–482 nm, where the CS2+ molecular ions were prepared purely by [3+1] multiphoton ionization of the neutral CS2 molecules at 483.2 nm. The PHOFEX spectrum was assigned essentially to the CS2+(A 2Πu)←CS2+(X 2Πg) transition, and the dissociation mechanism of CS2+ was preliminarily attributed to (i) CS2+(X 2Πg)→CS2+(A 2Πu) through one-photon excitation, (ii) CS2+(A 2Πu)→CS2+(X†) via internal conversion process due to the vibronic coupling between the A and X states, (iii) CS2+(X†)→CS2+(B 2Σu+) through the second photon excitation, and (iv) CS2+(B 2Σu+)→S++CS owing to the potential curve crossing with the repulsive 4Σ− state correlated with the first dissociation limit.

The (0,0), (0,1), (0,2), (0,3), (1,2), (1,3), (1,4) and (2,4) bands of the C1Σ–X 1Σ transition of YBr, between 720 and 765 nm, have been studied using the technique of laser vaporization/reaction with supersonic cooling and laser induced fluorescence spectroscopy. Spectra of both Y79Br and Y81Br isotopic molecules were observed and analysed. A merged least-squares fit of the measured line positions yield molecular constants for the = 0–2 levels of the C 1Σ state and the = 0–4 of the X1Σ state. The equilibrium bond length of the C1Σ state has been determined to be 2.6087(2) A.

Laser-induced fluorescence (LIF) excitation spectra of the CF2 A 1B1←X 1A1 system around 250 nm has been measured under supersonic free-jet conditions. CF2 radical was produced by DC-discharge of CF4 seeded in argon. Previously ambiguous assignments of the A-state stretching frequencies have been experimentally determined to be ν1′=1012.1 cm−1 and ν3′=1180.2 cm−1, by analyzing the subband spectra attributed to some of the observed progressions (20n, 10120n−2 and 20n311 (n≤6)) in which 21 vibronic bands were unambiguously labeled. The measured A-state stretching frequencies do not support King et al.'s assignments [D.S. King, P.K. Schenck, J.C. Stephenson, J. Mol. Spectrom. 78 (1979) 1], but are in good agreement with Cameron et al.'s theoretical assertions [M.R. Cameron, S.H. Kable, G.B. Bacskay, J. Chem. Phys., 103 (1995) 4475].

The resonance-enhanced multiphoton ionization (REMPI) of SO 2 in the range 365–405 nm has been studied using mass-distinguished excitation spectra. Most of the resonance peaks for both parent ion SO 2 + and fragment ions SO + , S + and O + in the excitation spectra have been assigned to the transition SO 2 ( a 3 B 1 ) ← SO 2 ( X 1 A 1 ) . It has been reasonably assumed that SO 2 (C 1 B 2 ), produced by the subsequent excitation of SO 2 (a 3 B 1 ), plays a key role in generating the fragment ions. It seems that tragment ions come mainly from the photoionization of neutral fragments dissociated from SO 2 (C 1 B 2 ) while the parent ion is formed directly by further photoionization of SO 2 (C 1 B 2 ). That the resonance peaks of the parent ion appear generally narrower than those of fragment ions can also be explained by the known spectral properties of SO 2 (C 1 B 2 ).

Rotational relaxation of CS2 in argon free jet was studied using laser‐induced fluorescence (LIF). The rotational populations were obtained from LIF detection at 19 different points along the jet axis from 3 to 15 nozzle diameters. On the basis of the energy gap power law, the master equation was solved to fit the experiment results, and the two temperature‐independent parameters in the law were determined. The results show that the state‐to‐state relaxation cross sections vary as the inverse 1.7 power of the energy gap between the initial and the final states. The expressions for the state‐to‐state relaxation cross sections and the rate constants were written. The relaxation cross sections decrease with increasing temperature over the range of 2–60 K for the CS2+Ar collision.