Nuclear Spin of Phosphorus from Band Spectrum Analysis

The emission spectrum of P₂ 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 1/2(h2π). 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 ¹Σ→¹Σ. The odd levels of the ground state have the greater statistical weight. The following molecular constants are obtained; Be'=0.2415 cm^-1; Be"=0.3058 cm^-1; α^'=0.00164; α^''=0.00165.