Watson James K. G.
Steacie Institute for Molecular Sciences, National Research Council of Canada, Ottawa, Ontario, K1A 0R6, Canada
J Mol Spectrosc. 2001 Jun;207(2):276-284. doi: 10.1006/jmsp.2001.8344.
Relative intensities in the vibrational structure of the Ã(1)A(u)(C(2h))-&Xtilde;(1)Sigma(+)(g)(D(infinityh)) electronic transition of acetylene are calculated. The calculation takes account of the large change of geometry and the change in the normal coordinates (the Dushinskií effect) between the two states. Because conventional vibrational wavefunctions for a nonlinear state do not behave correctly at linear geometries the vibrational integrals are only evaluated approximately. The transition ((1)Sigma(u)(-)-(1)Sigma(+)(g)) is forbidden at linear geometries, and so calculations are performed without and with a factor proportional to the angle of bend from linearity. Good agreement with experiment is obtained for the first few quanta of the absorption spectrum, lending support to the Ã-state harmonic potential of Tobiason et al., J. Chem. Phys. 99, 5762 (1993). Qualitative agreement is obtained for the emission spectrum (Jacobson and Field, J. Phys. Chem. 104, 3073 (2000)) when allowance is made for anharmonicity in the &Xtilde; state, but more quantitative agreement will require improvements in the empirical potential of the &Xtilde;-state, or an ab initio potential to higher energies than available at present. Copyright 2001 Academic Press.
计算了乙炔的Ã(1)A(u)(C(2h))-X̃(1)Σ+(g)(D∞h)电子跃迁振动结构中的相对强度。该计算考虑了两个态之间几何结构的巨大变化以及正则坐标的变化（杜什inski效应）。由于非线性态的传统振动波函数在线性几何结构下表现不正确，因此振动积分仅进行近似评估。(1)Σu(-)-(1)Σ+(g)跃迁在线性几何结构下是禁阻的，所以分别在不考虑和考虑与偏离线性的弯曲角成正比的因子的情况下进行计算。对于吸收光谱的前几个量子，计算结果与实验结果吻合良好，这支持了托比亚松等人（《化学物理杂志》99, 5762 (1993)）提出的Ã态谐振子势。当考虑X̃态的非谐性时，发射光谱（雅各布森和菲尔德，《物理化学杂志》104, 3073 (2000)）得到了定性的吻合，但要获得更定量的吻合，需要改进X̃态的经验势，或者将从头算势扩展到比目前可用能量更高的范围。版权所有2001年学术出版社。
