The new investigation of the [formula omitted] system of AlH

Abstract

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 0.005cm−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 versusN(N+1) for the v=1 level.