The Low-Lying States of He2.

The near-infrared emission spectrum of He2, excited in a Be hollow cathode discharge, has been recorded at high resolution using a Fourier transform spectrometer. The c3Sigma+g-a3Sigma+u (0-0, 1-1, 2-2, 1-0, and 2-1) and C1Sigma+g-A1Sigma+u (0-0 and 1-1) transitions have been observed in the 9000-15 000 cm-1 spectral region. A global analysis of the six lowest excited states of He2 (c3Sigma+g, b3Pig, a3Sigma+u, C1Sigma+g, B1Pig, and A1Sigma+u) was carried out by combining our measurements with previously reported infrared data for the b3Pig-a3Sigma+u system [S. A. Rogers et al., Mol. Phys. 63, 901 (1988)] and with laser measurements for the B1Pig-A1Sigma+u transition [H. Solka et al., Mol. Phys. 60, 1179 (1987)]. To account for the fine structure in the a3Sigma+u state, high precision r.f. measurements were included in the global fit. A consistent set of improved molecular constants was derived for the c3Sigma+g (v = 0, 1, and 2), b3Pig (v = 0 and 1), a3Sigma+u (v = 0, 1, and 2), C1Sigma+g (v = 0 and 1), B1Pig (v = 0 and 1), and A1Sigma+u (v = 0 and 1) levels. A study of the vibrational dependence of these constants was also performed, leading to the equilibrium parameters for the six electronic states. Copyright 1998 Academic Press.