The emission spectrum of the C1Σ+-X1Σ+ system of AlH

The ultraviolet spectrum of AlH has been investigated at high resolution between 42 000 and 45 000 cm−1 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 NH3. The emission from the discharge was observed with a plane grating spectrograph and recorded by a photomultiplier tube. The 0-0, 1-1 and 1-2 bands of the C1Σ+-X1Σ+ transition have been identified and rotationally analyzed. The new data were elaborated with help of recent X1Σ+ state parameters reported by White et al. [J. Chem. Phys. 99 (1993) 8371-8378] and by Szajna and Zachwieja [Eur. Phys. J. D. 55 (2009) 549-555]. Determined constants of the excited C1Σ+ state include: Te = 44 675.3711(57) cm−1, ωe = 1575.3357(42) cm−1, ωexe = [125.5] cm−1, Be = 6.66804(32) cm−1, αe = 0.55839(56) cm−1, De = 2.23(13) × 10−4 cm−1, βe = 6.13(25) × 10−4 cm−1 and re = 1.613132(39)  Å. The C1Σ+ state is found to be extensively perturbed in the v = 0 and 1 vibrational level at J = 20, 22 − 27 and J = 5 − 9, respectively. This was probably caused by the interaction with the vibrational levels of the outer minimum.