Predissociation and Pressure Effects in the Band Spectrum of Aluminium Hydride

Abstract

BY the aid of graphical methods¹, we have constructed the potential curves V_j(r) for different rotational states of ¹II in aluminium hydride. From estimations on the line width of the diffuse lines in the ¹II; ¹ band system, we were able to extend our constructions to wide nuclear spacing (r 3 × 10⁸ cm.) as shown in Fig. 1. Reproducing the curve we found, that even now a potential barrier remains in ¹II, the height of which is 400 cm.¹, as related to the limit of dissociation. This result appears somewhat surprising, as in the few cases hitherto investigated (hydrogen, mercury hydride, etc.) a smooth approach of the potential curves to the limit of dissociation has been assumed. We are not in the position to distinguish between the alternatives, whether this barrier is a feature of the ¹II–state itself or produced by the intersection of some unknown and repulsive ¹II*;–state, as suggested in Fig. 1. In the latter case, the actual ¹II–curve should be correlated to some excited state in the Al atom as already suggested by Kronig², although for other reasons. In any event, by this construction the level scheme of AlH has been related to that of the Al atom, the position of the level = 0, J = 0 in ¹II situated 1400 ± 50 cm¹ below the limit of dissociation. Incidentally, it may be mentioned that some interesting cases of perturbations and predissociations in the excited ¹ and ¹ states⁴ are readily explained hereby.