High-resolution studies of total electron excitation functions near threshold for the statesBΣu+1andcΠu3of molecular hydrogen

Studies have been made of uv and metastable excitation functions for ${\mathrm{H}}_2$ near threshold. Within 2 eV of threshold the total cross sections appear to be dominated by two vibrational series of resonances. In the excitation function of $B{}_{}{}^1{}_{}{}^{}\Sigma _u^{+}{}_{}{}^{}$ (uv emitting), one series (band "$a$") is ten times more intense than the other (band "$c$"), while for $c{}_{}{}^3{}_{}{}^{}\Pi _u^{}{}_{}{}^{}$ excitation (metastable), the two series have approximately equal intensity. The measured energy positions of the resonant peaks agree well with results obtained by other experimental techniques and with theory. Energy calibration of the metastable excitation function has confirmed that the $c{}_{}{}^3{}_{}{}^{}\Pi _u^{}{}_{}{}^{}\mathrm{}(v=0\mathrm{})\mathrm{}$ level is metastable, and there was no obvious threshold for a second metastable vibrational level, although the nature of the data does not preclude its existence.