Electronic absorption and resonance Raman spectroscopy from ab initio quantum molecular dynamics
Electronic absorption and resonance Raman spectroscopy from ab initio quantum molecular dynamics
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DOI：
10.1021/jp992197r
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发表时间：
1999-12-09
影响因子：
2.9
通讯作者：
Martínez, TJ
中科院分区：
文献类型：
--
作者：
Ben-Nun, M;Martínez, TJ
使用从头多重生成 (ALMS) 方法和相关函数方法，根据第一原理分子动力学计算 pi --> pi* 激发并充分考虑非谐性和 Duschinsky 旋转效应的乙烯吸收和共振拉曼激发曲线。 AIMS 方法同时求解核和电子薛定谔方程，并将唯一的核波函数与每个电子态相关联。计算出的吸收光谱的半峰全宽为9800+/-1300cm(-1)(与实验值9500cm(-1)一致)，并且由于C=C拉伸而具有间隔800+/-10cm(-1)的高频结构。共振拉曼激发曲线在所有完全对称模式中都表现出基本活性，其中 C=C 拉伸模式是最主要的。此外，在扭转运动、面外摇摆运动和面外摇摆运动中观察到泛音活动。该活性与第一激发态扭曲且其中一个 CH2 基团金字塔化的观察结果一致。研究了电子跃迁偶极子的坐标依赖性，我们发现它对扭转坐标的依赖性很强，而对金字塔化和 C=C 拉伸坐标的依赖性较小。然而，在本文使用的近似值内，这种依赖性不会显着影响光谱，并且康登近似值相当准确。
The absorption and resonance Raman excitation profiles of ethylene following pi --> pi* excitation and taking full account of anharmonicity and Duschinsky rotation effects are calculated from first principles molecular dynamics using the ab initio multiple spawning (ALMS) method and a correlation function approach. The AIMS method solves the nuclear and electronic Schrodinger equations simultaneously and it associates a unique nuclear wave function with each electronic state. The computed absorption spectrum has a full width at half maximum of 9800 +/- 1300 cm(-1) (in agreement with the experimental value, 9500 cm(-1)) and a high-frequency structure spaced by 800 +/- 10 cm(-1) attributed to C=C stretching. The resonance Raman excitation profile exhibits fundamental activity in all totally symmetric modes with the C=C stretching mode being the most dominant. In addition, overtone activity is observed in the torsional motion, out-of-plane wagging motions and the out-of-plane rocking motions. This activity is consistent with the observation that the first excited state is twisted and one of the CH2 groups is pyramidalized. The coordinate dependence of the electronic transition dipole is investigated, and we find that it depends very strongly on the torsional coordinate and less so on the pyramidalization and C=C stretching coordinates. However, within the approximations used in this paper this dependence does not influence the spectra significantly and the Condon approximation is quite accurate.