Ma Xing-Xiao

Studies of V—T/R relaxation in polyatomic molecules with a time-resolved thermal lens

Abstract The V—T/R overall relaxation rates of some polyatomic molecules were measured by means of a thermal lens. It is found that the rates are rather fast

Deuterium separation by multiphoton dissociation of dichlorofluoromethane

Absorption and dissociation probabilities of CHCl2F and CDCl2F were investigated by a pulsed CO2 laser in the wavenumber region of largest selectivity for deuterium. The absorption of CHCl2F, which is a difference band, can largely be suppressed by cooling. At 200 K and at 920 cm−1 absorption selectivities up to 4000 were found by extrapolation. In the presence of buffer gas, CDCl2F can be multiphoton excited nearly like a linear absorber (“harmonic oscillator”). This is interpreted by a nearly resonant collisional relaxation v7 to v2 and by the smallness of the cross anharmonicity x27. The dissociation selectivityS was 24,000 at natural abundance. Such large values were measured by a chromatographic method.S depends only onpD, the partial pressure of the deuterated species. This dependence is approximately ln S∝pD−1. It can be rationalized by considering only the average energy transferred to the nonresonant molecules by collisions with CDCl2F. The above functional shape is related to an Arrhenius type law. Comparison with trifluoromethane for D separation shows that CHCl2F has primarily two advantages: its rapid H-D exchange with water and the less stringent requirements of laser energy and pulse length.

The UV laser photolysis of stibine

Abstract The 403–700 nm emission spectrum observed in ArF laser photolysis of stibine was recorded for the first time and was assigned to the SbH 2 (A 2 A 1 → X 2 B 1 ) transition. More than fifty emission lines arising from the transitions of Sb(6s → 5p) were also observed.

Resonance-enhanced multiphoton ionization spectra of the halogen atoms

The resonance-enhanced multiphoton ionization (REMPI) spectra of atomic chlorine and bromine in the range of 230-245 nm and 250-285 nm were obtained by using REMPI and time of flight (TOF) techniques. There are twenty-six lines for Cl and twenty-three for Br in the spectra, among which five transitions of Cl and four of Br are observed for the first time. These lines are due to transitions from the Cl(3p 2P3/20, 2P1/20) and Br(4p 2P3/20, 2P1/20) states to upper states induced by two-photon excitation. It is found that the Stark shift of different excited states are almost the same, and they are independent of the S, L, and J quantum numbers of the excited state.

Quantum Beat Spectroscopy of SO2 in the 235-224 nm Range

Using time-resolved laser-induced fluorescence(LIF) spectroscopy, the fluorescence quantum beat decay was observed in (1B2) ← (1A1) transition of SO2 molecule. The experimental results show that only thev3 mode and its combination band v1 + v2 + v3 excitation exist the beat decay. Analyzing the result, we attribute the quantum beat states to the coupling of the v3 vibration mode of state with the high vibrational levels of the electronic ground state.

An approach of estimating excitation cross sections in multiphoton processes

We suggest a simple approach to roughly estimate the excitation cross sections of various steps in a multiphoton ionization (or dissociation) process by applying the measured dependence of product signal on laser intensity. The validity of this method is demonstrated theoretically by means of the rate equations based upon a two-step kinetic model and can, in principle, be extended to the multiphoton process with steps more than two. Some results of numerical test and experiment are quoted.

GAS DYNAMIC PROBLEMS CAUSED BY THE GENERATION OF THE RADICALS IN A SUPERSONIC JET

A simplified one-dimensional model was proposed to treat the gas dynamic problems in a supersonic jet, which was used to produce radicals cooled by supersonic expansion. Based on this model, the gas dynamic equations can be integrated directly to obtain the evolution of the translational temperature and the rotational temperature of free radicals as well as the molecule density. The results show that the heating position where the radicals are generated and the initial rotational temperature of radicals have little effect on the rotational temperature at the down stream detection point, if the heating position is close to the nozzle orifice.

束-气条件下He(2 3 S )与CH 3 Cl及CH 3 I的传能研究

The energy transfer readies from lie(VS) to CH3Cl and CH3I have been studied in a beam gas condition by observing the emission of the excited state products. The formation rate constants of CH(A), CH(B) and CH(C) produced by He(2(3)S) with CH3Cl or CH3I were determined. The nascent rovibrational distrbution of CH(A(2)Delta, v(1) = 0 2) anti CH(B-2 Sigma(-), v(1) = 0) from above reactions were obtained by a computer simulation of CH(A - X, B - X) emission. The experimental results showed that the major of the reaction available energies is deposited into the translation energies or the products. The mechanism of the energy transfer reactions from He(2(3)S) to CH3CI and CH3I were also discussed.