Spectroscopic Study of the C 1Σ+ State of 6LiH and 7LiD

Abstract

The C 1Σ+ excited electronic state of 6LiH and 7LiD isotopomers has been studied by a pulsed optical−optical double resonance fluorescence depletion spectroscopic technique, in which a band-resolved laser-induced fluorescence detection scheme was used. Forty-two 6LiH vibrational (v = 2−43) levels and fifty-five 7LiD vibrational (v = 4−58) levels have been separately observed. The absolute vibrational numbering of the 7LiD C 1Σ+ state is identified via a comparison between observed term values and those calculated with a hybrid potential energy curve reported previously for the 7LiH C 1Σ+ state. Among the highest observed vibrational levels, the highest observed rovibrational levels are respectively the (43,5) level for 6LiH and the (58,8) level for 7LiD, compared to the level (43,8) reported previously for the 7LiH case. The spectral term values for the vibrational levels lying above v = 33 for 6LiH, and those above v = 44 for 7LiD, occur in an irregular order. The v = 34, J = 0 level of 6LiH and the v = 45, J = 0 level of 7LiD lie mainly in the inner, small well. The term values for the observed rovibrational levels, for 2 ≤ v ≤ 32, 0 ≤ J ≤ 11 of 6LiH and for 4 ≤ v ≤ 44, 0 ≤ J ≤ 13 of 7LiD, in the outer ionic well are described by a set of Dunham-type coefficients. Together with previous observed term values of 7LiH, a combined isotopomer Dunham-type analysis has been performed, and five hydrogen and three lithium mass-dependent Born−Oppenheimer breakdown correction terms for the C 1Σ+ state are determined.