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

Abstract

The C 1 Σ + excited electronic state of 6 LiH and 7 LiD 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 6 LiH vibrational ( v = 2−43) levels and fifty-five 7 LiD vibrational ( v = 4−58) levels have been separately observed. The absolute vibrational numbering of the 7 LiD C 1 Σ + state is identified via a comparison between observed term values and those calculated with a hybrid potential energy curve reported previously for the 7 LiH C 1 Σ + state. Among the highest observed vibrational levels, the highest observed rovibrational levels are respectively the (43,5) level for 6 LiH and the (58,8) level for 7 LiD, compared to the level (43,8) reported previously for the 7 LiH case. The spectral term values for the vibrational levels lying above v = 33 for 6 LiH, and those above v = 44 for 7 LiD, occur in an irregular order. The v = 34, J = 0 level of 6 LiH and the v = 45, J = 0 level of 7 LiD lie mainly in the inner, small well. The term values for the observed rovibrational levels, for 2 ≤ v ≤ 32, 0 ≤ J ≤ 11 of 6 LiH and for 4 ≤ v ≤ 44, 0 ≤ J ≤ 13 of 7 LiD, in the outer ionic well are described by a set of Dunham-type coefficients. Together with previous observed term values of 7 LiH, 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 1 Σ + state are determined.