The Band Spectrum of Ionized Aluminum Hydride

The Schüler hollow aluminum cathode lamp, containing helium and hydrogen, maintained at 2000 volts d.c., has been used to excite the band spectrum of AlH, which has been photographed with a 21-foot grating spectrograph. Among the new systems appearing there is one with principal head at 3632A which on analysis proves to consist of the (0,0) and (1,1) bands of a ${}_{}{}^2{}_{}{}^{}\Pi \left(\mathrm{regular}\right)\to {}_{}{}^2{}_{}{}^{}\Sigma _{}^{+}{}_{}{}^{}$ system due to Al${\mathrm{H}}^{+}$. The ${}_{}{}^2{}_{}{}^{}\Pi$ state is found to be regular and not inverted as suggested by Holst. The various band constants are obtained and the spin and $\Lambda$-doubling compared with theory.