Emission spectroscopy of the A1Π–X1Σ+ system of AlH

Abstract

The high-resolution emission spectrum of the A1 Π–X1Σ+ transition of AlH was observed in the 18 000–25 000 cm-1 spectral region using a conventional spectroscopic technique. The AlH molecules were excited in an Al hollow-cathode lamp filled with a mixture of Ne carried gas and a trace amount of NH3. The emission from the discharge was observed with a plane grating spectrograph and recorded by a photomultiplier tube. In total 163 transition wave numbers belonging to six bands (0-0,1 and 1-0,1,2,3) were precisely measured and rotationally analysed. In the final fit the present data have been combined with available high-resolution measurements of the vibration-rotation bands by White et al. [J. Chem. Phys. 99, 8371 (1993)]. This procedure enabled extracting molecular constants for the A1 Π and X1 Σ+ states of AlH. A very slight local perturbation has been discovered in the v=1 vibration level of the A1 Π state at J=5. This was probably caused by the interaction with the a3Π state.