Ro-vibrational level dependence of the radiative lifetime of the Na2 41Σg+ shelf state

Abstract

We report on calculations—using the LEVEL and BCONT programs by Le Roy, the latter of which is a version modified by B. McGeehan—of the dependence of the radiative lifetime of the Na2 sodium dimer 41Σg+ shelf-state on the initial vibrational and rotational level for corresponding quantum numbers of 0 ≤ v ≤ 75 and 0 ≤ J ≤ 90, respectively. We also present experimental lifetime values for 43 < v < 64, averaged over J = 19 and 21, obtained by a delayed pump-probe method using a previously described molecular beam and time-of-flight apparatus. Our calculated results are based on all possible dipole allowed transitions (to the 21Σu+, 1(B)1Πu, and 1(A)1Σu+ electronic states) terminating into bound as well as free final states. The shelf of the initial electronic state is a consequence of configuration interaction with the lowest Na+–Na− ion-pair potential and occurs, for the rotationless molecule, at the vibrational level v = 52. From the 41Σg+ vibrational ground state to the shelf, the calculated lifetimes increase monotonically by a factor of about 3.8. Beyond around v = 52, depending on rotational excitation, the lifetimes decrease, settling to a value intermediate to the maximum and the minimum at v = 0. Within error bars and in the range available, our experimental data are compatible with these findings. In addition, our calculations reveal unusual and pronounced oscillatory variation of the lifetime with rotational quantum numbers for fixed vibrational levels above—but not below—the shelf. We discuss our findings in terms of the appropriate transition dipole moments and wavefunctions and provide a detailed comparison to recent lifetime calculations of sodium dimer ion-pair states [Sanli et al., J. Chem. Phys. 143, 104304 (2015)].

Rovibrationally resolved radiative lifetime and collisional cross section measurements of the 61Σg+(v=6,Wagle1, Pant2, Converse3 et al. 2021Journal of Quantitative Spectroscopy and Radiative Transfer0000View full textAdd to dashboardCite

“…The measured radiative lifetimes of Na 2 6 1 Σ + g (v=8,J=31) and 6 1 Σ + g (v=6,J=31) (even vibrational states) are in excellent agreement with each other but both are smaller compared to the 6 1 Σ + g (v=7,J=31) (odd vibrational state) [12]. Similar lifetime variations in the Na 2 4 1 Σ + g state were reported [14]. Hence, considerable differences in lifetimes for the v=6, 8 quantum numbers will be further investigated.…”

Time-Resolved Vibrational Spectroscopy to Measure Lifetime of the E$^3Π_g(v=3)$ state of Molecular Iodine

“…On the other hand, measurements of a long sequence of lifetimes as a function of (v, J) can reveal scaling laws in these quantities. Recently published articles reported a strong dependence of molecular lifetime on rovibrational level's wavefunctions [33,34]. This work will be followed by making series of lifetime measurements as a function of vibrational or rotational quantum numbers in diatomic molecules.…”

“…This is specifically important because the E-state correlates diabatically with the ground state I − ( 1 S o )+I + ( 3 P 2 ) of the separated ions and diabatic dissociation limit corresponds to about 72000 cm −1 [32]. Recently, calculated radiative lifetimes for the alkali dimer ion pair states have revealed strong variations as a function of internuclear distance because of the effect of the ion pair potentials [28,33,34].…”