Hu Zhengfa, Lee Wei-Bin, Zhang Xiao-Peng, Wei Pei-Ying, Lin King-Chuen
Department of Chemistry, National Taiwan University and Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106, Taiwan.
Chemphyschem. 2008 Feb 22;9(3):422-30. doi: 10.1002/cphc.200700620.
(1+1) Resonance-enhanced multiphoton ionization (REMPI) spectra of CS(2) and molecular dissociation dynamics are investigated using a time-of-flight mass spectrometer equipped with velocity imaging detection. The REMPI spectra via a linear-bent 1Sigma(g)+-->(1)B(2)(1Sigma(u)+) transition are acquired in the wavelength range of 208-217 nm. Each ro-vibrational band profile of the (1)B(2)(1Sigma(u)+) state is deconvoluted to yield the corresponding predissociative lifetime from 0.3 to 3 ps. Upon excitation at 210.25 and 212.54 nm, the resulting images of S(+) and CS(+) fragments are analyzed to give individual translational energy distributions, which are resolved into two components corresponding to the CS+S((3)P) and CS+S((1)D) channels. The product branching ratios of S((3)P)/S((1)D) are evaluated to be 5.7+/-1.0 and 9.6+/-2.5 at 210.25 and 212.54 nm, respectively. Despite the difficulty avoiding the effect of multiphoton absorption, the molecular dissociation channel is verified to prevail over the dissociative ionization channel of CS(2). The anisotropy parameters for the triplet and singlet channels are determined to be approximately 0.8 and 1.1-1.3, respectively, suggesting that the predissociative state should have a bent configuration with a short lifetime.
利用配备速度成像检测的飞行时间质谱仪研究了CS₂的(1+1)共振增强多光子电离(REMPI)光谱和分子解离动力学。通过线性-弯曲的1Σg⁺→(1)B₂(1Σu⁺)跃迁获得的REMPI光谱在208-217nm波长范围内。对(1)B₂(1Σu⁺)态的每个转动-振动带轮廓进行去卷积，以得到0.3至3ps的相应预解离寿命。在210.25和212.54nm激发时，对所得的S⁺和CS⁺碎片图像进行分析，以给出各自的平动能分布，其被分解为对应于CS+S((³P))和CS+S((¹D))通道的两个分量。在210.25和212.54nm处，S((³P))/S((¹D))的产物分支比分别评估为5.7±1.0和9.6±2.5。尽管难以避免多光子吸收的影响，但分子解离通道被证实优于CS₂的解离电离通道。三重态和单重态通道的各向异性参数分别确定为约0.8和1.1-1.3，这表明预解离态应具有短寿命的弯曲构型。
