Predoi-Cross A, Lees RM, Johns JWC
Physics Department, University of New Brunswick, Fredericton, New Brunswick, E3B 5A3, Canada
J Mol Spectrosc. 1998 Oct;191(2):348-361. doi: 10.1006/jmsp.1998.7636.
We present in this work a high-resolution Fourier transform infrared study of the OH-bending vibrational band of 13CH3OH. We have investigated the 1070-1400 cm-1 spectral region at 0.002 cm-1 resolution using the modified Bomem DA3.002 Fourier transform spectrometer at the Steacie Institute for Molecular Sciences at the National Research Council of Canada in Ottawa. This study has led to (i) determination of excited-state J(J + 1) subband expansion coefficients and (ii) characterization of a variety of interactions coupling the different vibrational modes, notably a strong Fermi resonance between the OH bend and the torsionally excited CH3-rocking mode. The OH-bending band is widely spread with Q subbranches grouped in two peaks at about 1312 and 1338 cm-1. The lower levels for all assigned subbands were confirmed using closed loops of IR and FIR transitions. The subbands have been fitted to J(J + 1) power-series expansions in order to obtain the subband origins and the state-specific energy expansion coefficients for both the OH-bending and excited torsional CH3-rocking states. The strong interaction between the OH-bending state and the first excited torsional CH3-rocking state gives rise to several "extra" forbidden subbands due to intensity borrowing. The asymmetry splitting of the (ntauK) v = (122)OH A OH-bending doublet was found to be anomalously small, and the splitting of the (122)rA CH3-rocking doublet is observed to be enhanced. We have identified a network of intermode interactions causing this unusual behavior, but a quantitative analysis of the vibrational coupling is restricted by limited knowledge of the unperturbed positions of the interacting levels. All these interactions provide relaxation channels for intramolecular vibrational redistribution among the lower vibrational modes in 13CH3OH. Another important finding is that the torsion-K-rotation energy curves in the OH-bending state display an inverted pattern compared to the ground state. Copyright 1998 Academic Press.
我们在这项工作中展示了对(^{13}CH_3OH)的(OH)弯曲振动带的高分辨率傅里叶变换红外研究。我们使用位于渥太华的加拿大国家研究委员会斯泰西分子科学研究所的改良型博梅DA3.002傅里叶变换光谱仪，在(0.002 cm^{-1})的分辨率下研究了(1070 - 1400 cm^{-1})的光谱区域。这项研究导致了：（i）确定激发态(J(J + 1))子带扩展系数；（ii）表征了耦合不同振动模式的多种相互作用，特别是(OH)弯曲与扭转激发的(CH_3)摇摆模式之间的强费米共振。(OH)弯曲带广泛分布，(Q)支在约(1312)和(1338 cm^{-1})处聚集成两个峰。所有指定子带的较低能级通过红外和远红外跃迁的闭环得以确认。为了获得(OH)弯曲和激发扭转(CH_3)摇摆态的子带起源和特定状态能量扩展系数，已将子带拟合为(J(J + 1))幂级数展开。由于强度借用，(OH)弯曲态与第一激发扭转(CH_3)摇摆态之间的强相互作用产生了几个“额外”的禁戒子带。发现((n_{\tau}K) v = (122)OH) (A) (OH)弯曲双峰的不对称分裂异常小，并且观察到((122)rA) (CH_3)摇摆双峰的分裂增强。我们已经确定了导致这种异常行为的模间相互作用网络，但由于对相互作用能级的未受扰动位置了解有限，对振动耦合的定量分析受到限制。所有这些相互作用为(^{13}CH_3OH)中较低振动模式之间的分子内振动再分布提供了弛豫通道。另一个重要发现是，与基态相比，(OH)弯曲态中的扭转 - (K) - 转动能量曲线呈现出倒置模式。版权所有1998年学术出版社。
