The low-lying states of He2

The near-infrared emission spectrum of He-2, excited in a Be hollow cathode discharge, has been recorded at high resolution using a Fourier transform spectrometer. The c(3) Sigma(g)(+) - a(3) Sigma(u)(+) (0-0, 1-1, 2-2, 1-0, and 2-1) and C-1 Sigma(g)(+) - Alpha(1) Sigma(u)(+) (0-0 and 1-1) transitions have been observed in the 9000-15000 cm(-1) spectral region. A global analysis of the six lowest excited states of He-2 (c(3) Sigma(g)(+), b(3) Pi(g), a(3)Sigma(u)(+), C(1)Sigma(g)(+), B(1)Pi(g), and A(1)Sigma(u)(+)) was carried out by combining our measurements with previously reported infrared data for the b(3)Pi(g) - a(3)Sigma(u)(+) system [S. A. Rogers et al; Mol. Phys. 63, 901 (1988)] and with laser measurements for the B(1)Pi(g)-A(1)Sigma(u)(+) transition [H. Solka et al., Mel. Phys. 60, 1179 (1987)]. To account for the fine structure in the a(3)Sigma(u)(+) state, high precision r.f. measurements were included in the global fit. A consistent set of improved molecular constants was derived for the c(3) Sigma(g)(+) (nu = 0, 1, and 2), b(3)Pi(g) (nu = 0 and 1), a(3) Sigma(u)(+) (nu = 0, 1, and 2), C(1)Sigma(g)(+) (nu = 0 and 1), B1 Pi(g) (nu = 0 and 1), and A(1)Sigma(u)(+) (nu = 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. (C) 1998 Academic Press.