Observation and analysis of the 21Σg+ state of 7Li2

Abstract

Upon excitation of 6Li2 or 7Li2 into the B1Πu state by the 476.5-, 488.0-, and 514.5-nm lines of an Ar+ laser, a new band system has been observed in emission in the 3500- to 7000-cm−1 by Fourier transform spectroscopy. These bands are shown to belong to the 21Σu+ → A1Σu+ system and to result from electronically inelastic B1Πu → 21Σg+ collisions. Absolute rotational and vibrational assignments are established and the following principal molecular constants for 7Li2 are derived from the spectra (two standard deviations in parentheses): Te=20101.580(20) cm−1 relative to the minimum of X1 σ1g Be=0.36044(2)cm−1 αe=4.17 (4) × 10−3cm−1 ωe=128.670(45)cm− ωeξe=1.70(3)cm−1 Re=3.6513(2)A De=3318.86(66) cm−1 The molecular constants for the 21Σg+ state are in good agreement with ab initio calculations. Significant Li+(1S) + Li−(2s21S) ion pair character of the outer limb of the 21Σg+ potential curve is reflected in an anomalous increase in ΔG versus v.