High-resolution FT-VIS emission spectroscopy of the A1Π−X1Σ

An extensive high-resolution visible wavelength emission spectrum of AlH, that covers eight bands of the A1Π−X1Σ+ 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 X1Σ+, ν=0−4 and A1Π, ν=0,1 levels. Also derived were rotational term values for the A1Π, ν=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 (Ykl) for the A1Π state of AlH were determined for the first time. A very small shifts of the A1Π, ν=0,J=17 and ν=1,J=5 levels have been observed and identified as result of the possible interaction between A1Π and 3Σ+ states.