Fine Structure of the Visible Absorption Bands of Bromine

A group of bands (from $v^{\prime }=7\mathrm{}$ to $v^{\prime }=13\mathrm{}$, $v^{\prime \prime }=2, 3 \mathrm{and} 4$) in the main absorption band system of bromine (${\mathrm{Br}}_2^{79,81}$) have been analyzed and found to consist of $P$ and $R$ branches only. Branches of the less abundant molecules, ${\mathrm{Br}}_2^{79}$ and ${\mathrm{Br}}_2^{81}$, showing alternating intensities, have been identified in several cases but owing to insufficient resolution a quantitative determination of the ratio of intensities has not been possible. An accurate calculation of the vibrational isotope shift of band origins has confirmed the quantum numbering previously deduced by the writer from measurements of band heads. The numerical values of the vibrational constants have been revised slightly from data on band origins. The analysis gave the following rotational constants for the ${\mathrm{Br}}_2^{79,81}$ molecule: