Nonadiabatic coupling in the 3Π3 and 4Π3 states of NaK

Abstract

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.

Spin–orbit coupling of the NaK 33Π and 31Π states: Determination of the coupling constant and observation of quantum interference effects

“…Heteronuclear alkali molecules have permanent dipole moments and are, therefore, of particular interest because, in principle, they can be oriented in an optical lattice [1][2][3][4][5][6][7]. In our laboratory at Lehigh University we have carried out a series of high-resolution spectroscopic studies of various excited electronic states of the heteronuclear alkali diatomic molecule NaK [8][9][10][11][12][13][14][15][16][17]. We have been particularly interested in the fine and hyperfine structure of these states and how variations in these structures with vibrational and rotational quantum numbers reflect changes in the electronic wavefunction with internuclear separation.…”

Effects of spin–orbit coupling on the coupled and excited states of NaK

“…The MCSCF orbitals were then used to calculate the singlet and triplet electronic wavefunctions using a full configuration interaction (CI) for the two valence electrons in a space of 86 orbitals. The basis set was Dunning's triple-zeta valence (TZV) [13], augmented to include long range orbitals [6] for a better description of excited states. The added orbitals are listed in Table 1.…”

“…Panel (a) shows values calculated using vibrational wavefunctions determined from the present ab initio potential curve. Panel (b) shows corresponding results using vibrational wavefunctions determined from the fitted potential curves of Miles et al [6]. In both cases, the theoretical spin-orbit interaction from the present work was used.…”

“…Several recent high-resolution spectroscopic studies in our laboratory have probed the fine and hyperfine structure of various excited triplet states of the NaK molecule [1][2][3][4][5][6]. Other studies have addressed singlet-triplet spin-orbit coupling [3,[7][8][9].…”

“…Previous studies [4,6] measured the rovibrational energy levels of the 3 3 P state and accurately determined the double well shape of that electronic potential. Morgus et al [4] noticed unusual oscillatory structure in the dependence of the rotational constants B v on the vibrational quantum number v that could be explained by the double well.…”