Huang Hong-Yi, Tsai Ming-Tsang, Lin King-Chuen
Department of Chemistry, National Taiwan University, Taipei 106 and Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106, Taiwan.
J Chem Phys. 2006 Apr 14;124(14):144302. doi: 10.1063/1.2181981.
With photolysis-probe technique, we have studied vibrational and rotational energy transfers of CH involving the B (2)Sigma(-) (v=1, 0<or=N<or=6, F) state by collisions with Ar, CO, and N(2)O. For the vibrational energy transfer (VET) measurements, the time-resolved fluorescence of the B-X(0,0) band is monitored following the (1,0) band excitation. For the rotational energy transfer (RET) measurements, the laser-induced fluorescence of the initially populated state is dispersed using a step-scan Fourier transform spectrometer. The time-resolved spectra obtained in the nanosecond regime may yield the RET information under a single pressure of the collider. The rate constants of intramolecular energy transfers are evaluated with simulation of kinetic models. The VET lies in the range of 4x10(-12) to 4x10(-11) cm(3) molecule(-1) s(-1), with efficiency following the order of Ar<CO<N(2)O, reflecting the average over Boltzmann rotational distribution. The RET rates are more rapid by one to two orders of magnitude, comparable to the gas kinetic, with the trend of Ar<CO<N(2)O. The transfer rates decrease with increasing N and DeltaN, proceeding via the DeltaN=-1 transitions slightly larger than DeltaN=+1. With the fine-structure labels resolved up to N=6, the fine-structure-conserving collisions prevail increasingly with increasing N in DeltaN not equal 0. The rate constants for the F(2)-->F(1) transitions are larger than the reverse F(1)-->F(2) transitions in DeltaN=0 for the Ar and CO collisions. The trend of fine-structure conservation is along the order of N(2)O<CO approximately Ar. For the CH-Ar collisions, the fine-structure conservation is less pronounced as compared with the v=0 level reported previously. In general, the propensity rules obeyed in the v=0 collision with Ar are valid in v=1, but the latter case shows a weaker tendency. It might be caused by the anisotropy difference of interaction potential when vibrational excitation is considered. For the polyatomic collider, the strong long-range dipole-dipole interaction may have the chance to vary the rotational orientation to increase the fine-structure-changing transitions.
利用光解探针技术，我们研究了处于B (2)Σ⁻ (v = 1, 0≤N≤6, F) 态的CH与Ar、CO和N₂O碰撞时的振动和转动能量转移。对于振动能量转移（VET）测量，在 (1,0) 带激发后监测B - X(0,0) 带的时间分辨荧光。对于转动能量转移（RET）测量，使用步进扫描傅里叶变换光谱仪对初始填充态的激光诱导荧光进行色散分析。在纳秒范围内获得的时间分辨光谱可以在单一碰撞气体压力下提供RET信息。通过动力学模型模拟评估分子内能量转移的速率常数。VET范围为4×10⁻¹²至4×10⁻¹¹ cm³·分子⁻¹·s⁻¹，效率顺序为Ar＜CO＜N₂O，反映了玻尔兹曼转动分布的平均值。RET速率快一到两个数量级，与气体动力学相当，趋势为Ar＜CO＜N₂O。转移速率随N和ΔN的增加而降低，通过ΔN = -1跃迁进行的过程略大于ΔN = +1。随着精细结构标记解析到N = 6，在ΔN≠0时，精细结构守恒碰撞随着N的增加而越来越占主导。对于Ar和CO碰撞，在ΔN = 0时，F(2)→F(1) 跃迁的速率常数大于反向F(1)→F(2) 跃迁。精细结构守恒的趋势顺序为N₂O＜CO≈Ar。对于CH - Ar碰撞，与先前报道的v = 0能级相比，精细结构守恒不太明显。一般来说，在v = 0与Ar碰撞中遵循的倾向规则在v = 1时仍然有效，但后一种情况的趋势较弱。这可能是由于考虑振动激发时相互作用势的各向异性差异所致。对于多原子碰撞气体，强的长程偶极 - 偶极相互作用可能有机会改变转动取向，以增加精细结构变化的跃迁。
