Darr Joshua P, Loomis Richard A, McCoy Anne B
Department of Chemistry, Washington University, Saint Louis, MO 63130, USA.
J Chem Phys. 2005 Jan 22;122(4):44318. doi: 10.1063/1.1829971.
The He...I (35)Cl intermolecular vibrational levels with n'=0-6 that are bound within the He+ICl(B,v'=3) potential [A. B. McCoy, J. P. Darr, D. S. Boucher, P. R. Winter, M. D. Bradke, and R. A. Loomis, J. Chem. Phys. 120, 2677 (2004)] are identified in laser-induced fluorescence experiments performed at very low temperatures within a supersonic expansion. Comparisons of the positions and intensities of these lines with the excitation spectra, calculated using potential surfaces to describe the interactions between the helium atom and ICl in its ground and excited state, assist in the assignments. Based on these comparisons the excited state potential was rescaled so that the experimental and calculated J'=0 energies agree to within the experimental uncertainties for all but the lowest, n'=0, intermolecular level. Two-laser, action, and pump-probe spectroscopy experiments indicate that the bound He...I (35)Cl(B,v'=3) intermolecular vibrational levels undergo vibrational predissociation forming rotationally excited I (35)Cl(B,v'=2,j') products with distributions that depend upon the initial intermolecular vibrational level excited. Action spectra recorded in the ICl B-X, 2-0 region while monitoring the Deltav=0, I (35)Cl(B,v'=2) channel reveal two additional dissociation mechanisms for the He...I (35)Cl(B,v') excited state complexes: rotational predissociation of discrete metastable states lying slightly above the He+I (35)Cl(B,v'=2) asymptote and direct dissociation that occurs when the linear conformer is excited to the continuum of states above the same asymptote. The rotational predissociation pathway forms I (35)Cl(B,v'=2,j') products in all of the rotational states energetically accessible. The direct dissociation mechanism yields very cold rotational product state distributions; for instance, the average rotational energy in the product state distribution measured when the linear complexes are prepared 20 cm(-1) above the dissociation limit is only 1.51 cm(-1), representing only 7.6% of the available energy.
在超声速膨胀中极低温下进行的激光诱导荧光实验中，确定了He...I(35)Cl分子间振动能级，其中n' = 0 - 6，这些能级束缚在He⁺ICl(B, v' = 3)势阱内[A. B. McCoy, J. P. Darr, D. S. Boucher, P. R. Winter, M. D. Bradke, and R. A. Loomis, J. Chem. Phys. 120, 2677 (2004)]。将这些谱线的位置和强度与激发光谱进行比较，利用势面计算来描述基态和激发态下氦原子与ICl之间的相互作用，有助于进行归属。基于这些比较，对激发态势进行了重新标度，使得除了最低的分子间能级n' = 0外，实验和计算得到的J' = 0能量在实验不确定度范围内一致。双激光、作用光谱和泵浦 - 探测光谱实验表明，束缚的He...I(35)Cl(B, v' = 3)分子间振动能级经历振动预解离，形成转动激发的I(35)Cl(B, v' = 2, j')产物，其分布取决于最初激发的分子间振动能级。在监测Δv = 0、I(35)Cl(B, v' = 2)通道时，在ICl B - X、2 - 0区域记录的作用光谱揭示了He...I(35)Cl(B, v')激发态复合物的另外两种解离机制：略高于He⁺I(35)Cl(B, v' = 2)渐近线的离散亚稳态的转动预解离，以及当线性构象体被激发到高于同一渐近线的连续态时发生的直接解离。转动预解离途径形成能量上可及的所有转动态的I(35)Cl(B, v' = 2, j')产物。直接解离机制产生非常冷的转动产物态分布；例如，当线性复合物在离解离极限20 cm⁻¹以上制备时，产物态分布中测得的平均转动能量仅为1.51 cm⁻¹，仅占可用能量的7.6%。
