High-resolution FT-VIS emission spectroscopy of the A1-X1+system of AlH

An extensive high-resolution visible wavelength emission spectrum of AlH, that covers eight bands of the A(1) Pi - X-1 Sigma(+) system, has been observed with a Fourier-transform spectrometer for the first time. The 0 - 0, 1, 2 and 1 - 0,1, 2, 3, 4 bands were recorded with an instrumental resolution of 0.03 cm(-1). The best signal-to-noise ratio of 9000:1 was obtained for the strongest 0 - 0 band. In total, 259 ro-vibronic frequencies were measured with an absolute accuracy of about 0.0020 cm(-1). The experimental data were fitted using the PGOPHER program written by Western (2017). Molecular constants were derived for the X-1 Sigma(+), nu = 0 - 4 and A(1) Pi, nu = 0, 1 levels. Also derived were rotational term values for the A(1)Pi , nu = 0, 1 levels. The current data were combined with the previous ground state results of White et al. (1993) using the instruction called the constraints on parameters within PGOPHER. The Dunham parameters (Y-ki) for the A(1) Pi state of AlH were determined for the first time. A very small shifts of the A(1)Pi, nu = 0, j = 17 and nu = 1, j = 5 levels have been observed and identified as result of the possible interaction between A(1) Pi and 3 Sigma(+) states.