双色双共振-多光子电离光谱研究小分子的碰撞诱导转动能量转移

用双色双共振多光子电离光谱方法测量了NO分子A~(2∑+)(v=0)态的转动能量转移, 得到了由R-F能量转移导致的转动可分辨的弛豫光谱, 计算了转动态-态转移速率常数。用以转移能量为基础的指数和幂指数能隙模型, 对碰撞弛豫态分布进行计算机模拟, 并从计算值与实验值的比较讨论了能隙模型存在的不足。用同法对I_2分子B∏(O_u~+)态的测量, 得到由转动能量转移导致的谱线展宽及交叠并作了分析。

Collision-Induced Rotational Energy Transfer in Small Molecules by Double Resonance MPI Spectroscopy

Collision-induced rotational energy transfer in the A~2Σ~+(v=0) state of NO has been measured by two-color double resonance-multiphoton ionization spectroscopy. Rotationally resolved relaxation spectra have been obtained for initial rotational levels N_i=1,7,13. The state-to-state rotational energy transfer rate constants have been determined from the experimental spectra by means of the rate equations under single collision approximation. The rate constant decreases with increasing rotational-quantum-number change ΔN. Exponential- and power-gap scaling laws have been used to analyze the experimental results and it has been found that the power-law fitting is better than the exponential-law fitting, especially for N_i=1. It has to be pointed out that the relaxation spectra from different initial ortational levels cannot be fitted well with a single set of parameters for either energy-based law. This results indicates that in addition to the energy gap some factors related to molecular rotation, e.g. the rotation period to the collision time ratio, must be taken into consideration in the collision model in order to describe the rotational energy transfer in detail. Similar rotational relaxation spectrum has been observed in NO-Xe (1:4) collision system. R-T energy transfer is considered to be the dominant pathway in collision-induced energy transfer between NO* and NO molecules or between NO* molecule and Xe atom. In addition, the rotation relaxation in the B∏(O_u~+) state of I_2 has been studied by OODR-MPI and the observed spectral line broadening discussed.