Babikov Dmitri, Kendrick Brian K, Zhang Peng, Morokuma Keiji
Chemistry Department, Marquette University, Wehr Chemistry Building, Milwaukee, WI 53201, USA.
J Chem Phys. 2005 Jan 22;122(4):44315. doi: 10.1063/1.1824905.
An accurate theoretical prediction of the vibrational spectra for a pure nitrogen ring (cyclic-N(3)) molecule is obtained up to the energy of the (2)A(2)/(2)B(1) conical intersection. A coupled-channel approach using the hyperspherical coordinates and the recently published ab initio potential energy surface [D. Babikov, P. Zhang, and K. Morokuma, J. Chem. Phys. 121, 6743 (2004)] is employed. Two independent sets of calculations are reported: In the first set, the standard Born-Oppenheimer approximation is used and the geometric phase effects are totally neglected. In the second set, the generalized Born-Oppenhimer approximation is used and the geometric phase effects due to the D(3h) conical intersection are accurately treated. All vibrational states are analyzed and assigned in terms of the normal vibration mode quantum numbers. The magnitude of the geometric phase effect is determined for each state. One important finding is an unusually large magnitude of the geometric phase effects in the cyclic-N(3): it is approximately 100 cm(-1) for the low-lying vibrational states and exceeds 600 cm(-1) for several upper states. On average, this is almost two orders of magnitude larger than in the previously reported studies. This unique example suggests a favorable path to experimental validation.
在（2）A₂/（2）B₁锥形交叉点的能量范围内，得到了纯氮环（环状 - N₃）分子振动光谱的精确理论预测。采用了一种使用超球坐标和最近发表的从头算势能面[D. Babikov, P. Zhang, and K. Morokuma, J. Chem. Phys. 121, 6743 (2004)]的耦合通道方法。报告了两组独立的计算结果：第一组中，使用标准的玻恩 - 奥本海默近似，完全忽略几何相位效应。第二组中，使用广义的玻恩 - 奥本海默近似，精确处理了由于D₃h锥形交叉点引起的几何相位效应。根据正常振动模式量子数对所有振动状态进行了分析和归属。确定了每个状态下几何相位效应的大小。一个重要发现是环状 - N₃中几何相位效应的大小异常大：对于低振动状态约为100 cm⁻¹，对于几个较高状态超过600 cm⁻¹。平均而言，这比先前报道的研究结果几乎大两个数量级。这个独特的例子为实验验证提供了一条有利途径。
