Emission spectroscopy of AlH: the X1Σ+, A1Π and C1Σ+ states characteristics.

The visible spectrum of AlH has been investigated at high resolution between 20000 and 21500 cm1 using a conventional spectroscopic technique. The AlH molecules were formed and excited in an aluminium hollow-cathode lamp with two anodes, filled with a mixture of Ne carried gas and a trace of NH 3. The emission from the discharge was observed with a plane grating spectrograph and recorded by a photomultiplier tube. The 0-0 and 1-1 bands of the C1Σ+-A1∏ system and 0-2 band of the A1∏-X1Σ+ were identified at 21126, 21368 and 20276 cm1, respectively. In total 121 transition wave numbers belonging to three bands were precisely measured (with accuracy of ±0.003 cm-1) and rotationally analysed. The new data were elaborated with the help of recent X1Σ+ state parameters reported by White et al. and of the C1Σ+, A1∏ states constants reported by Szajna and Zachwieja. As a result of this merged analysis the set of the molecular parameters and rotational terms values for the three lower lying states of the AlH molecule have been significantly improved.