Lazarov G, Lyyra AM, Li L. Enhanced Access to the Dark Triplet States of (7)Li(2) through New Singlet-Triplet A(1)Sigma(+)(u) approximately b(3)Pi(u) Perturbation Window Levels: Perturbation-Facilitated Optical-Optical Double Resonance Study of the 2(3)Sigma(+)(g) State.
JOURNAL OF MOLECULAR SPECTROSCOPY 2001;
205:73-80. [PMID:
11148109 DOI:
10.1006/jmsp.2000.8238]
[Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Two new pairs of singlet-triplet A(1)Sigma(+)(u) approximately b(3)Pi(u) mixed levels of (7)Li(2) have been observed and used here as "window" levels in cw perturbation-facilitated optical-optical double-resonance (PFOODR) experiments. Previously, only one b(3)Pi(u) vibrational level, v = 19, was known to mix with the singlet A(1)Sigma(+)(u) v = 13 level, resulting in three perturbed A approximately b pairs [L. Li, T. An, T.-J. Whang, A. M. Lyyra, W. C. Stwalley, R. W. Field, and R. A. Bernheim, J. Chem. Phys. 96, 3342 (1992)]. The scarcity of window levels and the resulting difficulty in accessing the dark triplet states of Li(2) is caused by the weak spin-orbit interaction of Li(2). The two new mixed b(3)Pi(u) v = 15 and 22 levels reported here enhance access to the dark triplet state manifold through expansion of the Franck-Condon overlap factor range. Furthermore, the earlier range of accessible rotational levels, N = 5, 7, and 10, is now expanded to include N = 8 and N = 16, thereby allowing for more reliable determination of the excited triplet states rotational structure. To demonstrate the importance of the new A(1)Sigma(+)(u) approximately b(3)Pi(u) mixed levels, we have studied the 2(3)Sigma(+)(g) state by cw PFOODR fluorescence excitation spectroscopy. New molecular constants and RKR potential curve have been determined. As previously reported [L. Li, G. Lazarov, and A. M. Lyyra, J. Mol. Spectrosc. 191, 387 (1998)], the 2(3)Sigma(+)(g) state interacts with the repulsive 1(3)Pi(g) state by L-uncoupling and predissociates. We show that some 2(3)Pi(g) levels predissociate accidentally by the 1(3)Pi(g) state via the 2(3)Sigma(+)(g) state through L-uncoupling. Copyright 2001 Academic Press.
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