The new investigation of the b3Σ−-a3Πsystem of AlH

- High-accuracy dispersive optical spectroscopy of the b3Σ−−a3Π system of AlH.
- Rotational analysis of the b-a, 0-0 and 1-1 bands.
- Improved molecular constants of the b3Σ− and a3Π states of AlH.
- Perturbations in the b3Σ−,v=0,1 levels.

The b3Σ−-a3Π visible system of AlH was observed at high resolution by using a high accuracy, dispersive optical spectroscopy technique. The emission spectrum was excited in an aluminum hollow-cathode lamp with two anodes, filled with a static Ne/NH3 gas mixture. In the 25,900-26,500cm−1 spectral region, the rotational structure of the two overlapped 0-0 and 1-1 bands was clearly observed and precisely measured. In total, 260 transition wavenumbers have been assigned with an estimated accuracy of about 0.005 cm−1. The open rotational structure of the Q branches in both bands has been measured for the first time, and the Λ-doubling in the a3Π,v=0,1 levels has been described by o,p and q parameters. For example, the values for the v=0 level are p0=1.754(14)×10−2cm−1, q0=3.264(28)×10−3cm−1 and o0=9.34(20)×10−2cm−1. Moreover, the spin-orbit interaction constants for the a3Π state have been obtained experimentally as follows: A0=40.6040(42)cm−1 and A1=40.419(59)cm−1. The a3Π,v=0,1 levels are considered as regular, while for the b3Σ−,v=0,1 levels considerable perturbations in the rotational structure have been observed. Consequently, these states have been represented in a different way in our least-squares treatment: a3Π state by molecular constants and b3Σ− state by term values. The observed irregularities in the b3Σ− state have been graphically described by plotting experimental minus calculated term values versus quantum number N for the v=0 level, as well as by plotting reduced term values versus N(N+1) for the v=1 level.

Rotational structure of the Q branches of the 0-0 and 1-1 bands of the b3Σ−-a3Π system of AlH.141