Takahashi Kaito, Sugawara Michihiko, Yabushita Satoshi
Department of Chemistry, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan.
J Phys Chem A. 2005 May 19;109(19):4242-51. doi: 10.1021/jp045041m.
To gain insight on the absorption intensities, as well as the direction of the transition moment for the OH stretching vibration in alcohols and acids, we performed detailed analyses for nitric acid, acetic acid, methanol, tert-butyl alcohol, water, and OH radical. We obtained both the potential energy surface and the dipole moment function (DMF) by the B3LYP method and performed quantum mechanical vibrational calculation using the grid variational method based on the local mode model. In this work, we employed the sum rule of the absorption intensities for the one-dimensional (1-D) vibrational Hamiltonian to construct an effective 1-D DMF, which is responsible for the total sum of the overtone intensities. The direction of this effective DMF was found to be tilted away from the OH bond by about 30 degrees for the polyatomic molecules. The nonlinearity of the DMFs in the directions parallel and perpendicular to the OH bond is discussed to rationalize the tilting. Furthermore, we analyzed the effective 1-D DMFs with the vibrational wave function expansion method and derived the effective portion of the 1-D DMF that is responsible for the overtone transition moment.
为了深入了解醇类和酸类中OH伸缩振动的吸收强度以及跃迁矩的方向，我们对硝酸、乙酸、甲醇、叔丁醇、水和OH自由基进行了详细分析。我们通过B3LYP方法获得了势能面和偶极矩函数（DMF），并基于局域模模型使用网格变分法进行了量子力学振动计算。在这项工作中，我们利用一维（1-D）振动哈密顿量的吸收强度求和规则构建了一个有效的1-D DMF，它负责泛音强度的总和。发现对于多原子分子，这个有效DMF的方向相对于OH键倾斜约30度。讨论了DMF在平行和垂直于OH键方向上的非线性，以解释这种倾斜现象。此外，我们用振动波函数展开法分析了有效的1-D DMF，并推导了负责泛音跃迁矩的1-D DMF的有效部分。
