Buser Michael, Frommhold Lothar
Physics Department, University of Texas, Austin, Texas 78712, USA.
J Chem Phys. 2005 Jan 8;122(2):024301. doi: 10.1063/1.1829055.
Existing measurements of the collision-induced rototranslational absorption spectra of gaseous mixtures of methane with helium, hydrogen, or nitrogen are compared to theoretical calculations, based on refined multipole-induced and dispersion force-induced dipole moments of the interacting molecular pairs CH4-He, CH4-H2, and CH4-N2. In each case the measured absorption exceeds the calculations substantially at most frequencies. We present the excess absorption spectra, that is the difference of the measured and the calculated profiles, of these supramolecular CH4-X systems at various gas temperatures. The excess absorption spectra of CH4-X pairs differ significantly for each choice of the collision partner X, but show common features (spectral intensities and shape) at frequencies from roughly 200 to 500 cm(-1). These excess spectra seem to defy modeling in terms of ad hoc exchange force-induced dipole components attempted earlier. We suggest that besides the dipole components induced by polarization in the electric molecular multipole fields and their gradients, and by exchange and dispersion forces, other dipole induction mechanisms exist in CH4-X complexes that presumably are related to collisional distortion of the CH4 molecular frame.
将甲烷与氦气、氢气或氮气的气态混合物的碰撞诱导旋转平移吸收光谱的现有测量结果与理论计算进行比较，该理论计算基于相互作用分子对CH4-He、CH4-H2和CH4-N2的精细多极诱导和色散力诱导偶极矩。在每种情况下，在大多数频率下，测量的吸收都大大超过计算值。我们展示了这些超分子CH4-X系统在不同气体温度下的过量吸收光谱，即测量曲线与计算曲线的差值。CH4-X对的过量吸收光谱因碰撞伙伴X的每种选择而有显著差异，但在大约200至500 cm(-1)的频率处显示出共同特征（光谱强度和形状）。这些过量光谱似乎无法用早期尝试的临时交换力诱导偶极分量来建模。我们认为，除了由分子电多极场中的极化及其梯度、交换力和色散力诱导的偶极分量外，CH4-X络合物中还存在其他偶极诱导机制，这些机制可能与CH4分子框架的碰撞畸变有关。
