Miles R D, Morgus L, Kashinski D O, Huennekens J, Hickman A P
Department of Physics, Lehigh University, Bethlehem, Pennsylvania 18015, USA.
J Chem Phys. 2006 Oct 21;125(15):154304. doi: 10.1063/1.2348635.
The excited 3 (3)Pi and 4 (3)Pi electronic states of the NaK molecule exhibit an avoided crossing, leading to the anomalous behavior of many features of the rovibrational energy levels belonging to each state. A joint experimental and theoretical investigation of these states has been carried out. Experimental measurements of the vibrational, rotational, and hyperfine structure of numerous levels of the 3 (3)Pi state were recently obtained using the Doppler-free, perturbation-facilitated optical-optical double resonance technique. Additional measurements for the 4 (3)Pi state as well as bound-free emission spectra from selected 3 (3)Pi, 4 (3)Pi, and mixed 3 (3)Pi to approximately 4 (3)Pi rovibrational levels are reported here. A model is also presented for calculating the mixed rovibrational level energies of the coupled 3 (3)Pi-4 (3)Pi system, starting from a 2x2 diabatic electronic Hamiltonian. The 3 (3)Pi and 4 (3)Pi potential curves and the coupling between them are simultaneously adjusted to fit the observed rovibrational levels of both states. The energy levels of the potential curves determined by the fit are in excellent agreement with experiment. The nonadiabatic coupling is sufficiently strong to cause an overall shift of 2-3 cm(-1) for many rovibrational levels as well as somewhat larger shifts for certain pairs of 3 (3)Pi to approximately 4 (3)Pi levels that would otherwise be very close together.
NaK分子的激发态3(3)Pi和4(3)Pi呈现出一个避免交叉，导致属于每个态的振转能级的许多特征出现异常行为。已对这些态进行了实验与理论的联合研究。最近，利用无多普勒、微扰辅助光-光双共振技术获得了3(3)Pi态多个能级的振动、转动和超精细结构的实验测量结果。本文报道了4(3)Pi态的额外测量结果以及从选定的3(3)Pi、4(3)Pi和混合的3(3)Pi到近似4(3)Pi振转能级的束缚-自由发射光谱。还提出了一个模型，用于从一个2×2非绝热电子哈密顿量出发计算耦合的3(3)Pi-4(3)Pi系统的混合振转能级能量。同时调整3(3)Pi和4(3)Pi势曲线及其之间耦合，以拟合两个态观测到的振转能级。拟合确定的势曲线能级与实验结果高度吻合。非绝热耦合足够强，导致许多振转能级整体位移2 - 3 cm(-1)，对于某些原本非常接近的3(3)Pi到近似4(3)Pi能级对，位移会更大一些。
