Xing Xi, Bahng Mi-Kyung, Reed Beth, Lam C S, Lau Kai-Chung, Ng C Y
Department of Chemistry, University of California, Davis, California 95616, USA.
J Chem Phys. 2008 Mar 7;128(9):094311. doi: 10.1063/1.2836429.
By using a high-resolution infrared (IR) laser to prepare propyne (C(3)H(4)) in selected rotational levels of the excited nu(1) (acetylenic C-H stretching) vibration mode prior to vacuum ultraviolet (VUV) laser pulsed field ionization-photoelectron (PFI-PE) measurements, we have obtained rotationally resolved VUV-PFI-PE spectra for the C(3)H(4) (+)(X (2)E(32,12),nu(1) (+)=1) band. The analysis of these PFI-PE spectra leads to the determination of the spin-orbit constant of A=-13.0+/-0.2 cm(-1) for the C(3)H(4) (+)(X (2)E(32,12),nu(1) (+)=1) state. Using this A constant and the relative rotationally selected and resolved state-to-state photoionization cross sections thus measured, we have obtained an excellent simulation for the VUV-PFI-PE origin band of C(3)H(4) (+)(X (2)E(32,12)), yielding a value of 83 619.0+/-1.0 cm(-1) (10.367 44+/-0.000 12 eV) for the adiabatic ionization energy of C(3)H(4) [IE(C(3)H(4))]. The present two-color IR-VUV-PFI-PE study has also made possible the determination of the C-H stretching frequencies nu(1) (+)=3217.1+/-0.2 cm(-1) for C(3)H(4) (+)(X (2)E(32,12)). The spectral assignment and simulation were guided by high-level ab initio calculations on the IE(C(3)H(4)), Franck-Condon factors for photoionization transitions, and rotational constants and vibrational frequencies for C(3)H(4) (+).
在真空紫外（VUV）激光脉冲场电离光电子（PFI - PE）测量之前，通过使用高分辨率红外（IR）激光将丙炔（C₃H₄）制备到激发的ν₁（炔烃C - H伸缩）振动模式的选定转动能级，我们获得了C₃H₄⁺（X²E₃₂,₁₂，ν₁⁺ = 1）能带的转动分辨VUV - PFI - PE光谱。对这些PFI - PE光谱的分析得出C₃H₄⁺（X²E₃₂,₁₂，ν₁⁺ = 1）态的自旋 - 轨道常数A = - 13.0±0.2 cm⁻¹。利用这个A常数以及由此测量的相对转动选择和分辨的态 - 态光电离截面，我们对C₃H₄⁺（X²E₃₂,₁₂）的VUV - PFI - PE起源带进行了出色的模拟，得出C₃H₄的绝热电离能[IE(C₃H₄)]为83619.0±1.0 cm⁻¹（10.36744±0.00012 eV）。目前的双色IR - VUV - PFI - PE研究还使得确定C₃H₄⁺（X²E₃₂,₁₂）的C - H伸缩频率ν₁⁺ = 3217.1±0.2 cm⁻¹成为可能。光谱归属和模拟由关于IE(C₃H₄)的高水平从头算计算、光电离跃迁的弗兰克 - 康登因子以及C₃H₄⁺的转动常数和振动频率指导。
