Nuclear Spin of Phosphorus from Band Spectrum Analysis

Abstract

The emission spectrum of ${\mathrm{P}}_2$ has been photographed in the first and second orders of the 21-foot grating. A strong alternation in intensity is observed in the successive rotational lines of many bands. The intensity ratio is found to be 3: 1, hence the nuclear spin of phosphorus is $\frac{1}{2}\left(\frac{h}{2\pi }\right)$. A fine structure analysis was made of the (6,22), (6,23), in addition to the (8,27), (8,28) and (9,28) bands previously reported by Herzberg. Only $P$ and $R$ branches are present. The transition involved is ${}_{}{}^1{}_{}{}^{}\Sigma \to {}_{}{}^1{}_{}{}^{}\Sigma$. The odd levels of the ground state have the greater statistical weight. The following molecular constants are obtained; Be'=0.2415 ${\mathrm{cm}}^{-1\mathrm{}}$; Be"=0.3058 ${\mathrm{cm}}^{-1\mathrm{}}$; ${\alpha }^{\prime }=0.00164\mathrm{}$; ${\alpha }^{\prime \prime }=0.00165\mathrm{}$.