Emission Bands in the3pΠcd1−1sΣ1System of the Hydrogen Molecule

The $3p{}_{}{}^1{}_{}{}^{}\Pi _{\mathrm{cd}}^{}{}_{}{}^{}-1s{}_{}{}^1{}_{}{}^{}\Sigma$ band system of the hydrogen molecule, heretofore observed only in absorption, has been discovered in emission. Ten bands from the first three vibrational levels of the excited state are analyzed and the rotational and vibrational constants are derived. The $d$ component levels of the $\Lambda$ type doubling are found to be strongly perturbed whereas the $c$ components appear to be quite regular. The most significant of the constants derived are as follows: $T_e=113908\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $B_e=30.56\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$ and ${\omega }_e=2353\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$.