Lifetimes and transition dipole moment functions of NaK low lying singlet states: Empirical and ab initio approach

Abstract

The paper presents experimental D 1∏ state lifetime τv′J′ data and develops empirical and ab initio approaches concerning D 1∏ and B 1∏ lifetimes, as well as D 1∏–X 1∑+, B 1∏–X 1∑+ and D 1∏–A 1∑+ transition dipole moment functions μ(R) of the NaK molecule. Experimental D 1∏(v′,J′) state τv′J′ values for v′ varying from 1 to 22 have been obtained from experimentally measured electric radio frequency-optical double resonance (rf-ODR) signal contours. The rf-ODR signals have been produced by D 1∏←X 1∑+ laser induced optical transition and rf field (1–900 MHz) induced e–f transition within the D 1∏(v′,J′) level. The possibility to determine empirical absolute μ(R) function in a wide R range from experimental τv′J′ dependence on v′ and J′ has been demonstrated; such an approach has been applied to obtain μ(R) for the B 1∏–X 1∑+ transition on which relative intensity data are absent. The empirical D 1∏–X 1∑+μ(R) function has been considerably improved by simultaneous fitting of relative intensity and lifetime data implicitly accounting for the J′ dependence of measured lifetime values. The finite-field technique combined with the many-body multipartitioning perturbation theory was used for ab initio all-electron transition moment calculations. This approach appeared to be adequate to compute reliable μ(R) functions due to a proper description of core-valence correlations. As a result, excellent agreement between ab initio and empirical B 1∏–X 1∑+ and D 1∏–X 1∑+ transition dipole moment functions has been achieved.