Isotope shift studies of the ultra-violet and visible bands of P16O and P18O

The spectra of P¹⁶O and P¹⁸O were excited in sealed discharge tubes containing neon (2–3 mm. pressure), oxygen gas enriched to 65 per cent. of¹⁸O and trace amounts of phosphorus vapour and photographed on a 3 m. grating spectrograph at a dispersion of 2·5 Å/mm. Isotope shift studies in theβ-bands confirmed the earlier vibrational scheme of Curryet al. and showed conclusively that the red as well as the violet degraded bands belonged to the sameβ-system. The present studies of isotope shifts also confirmed the vibrational assignments of the extensive ultraviolet bands involving the² Σ ^??X² Π transition and theγ-bands (A² Σ ⁺?X² Π). In the case of the visible bands, they provided evidence for the first time that the bands at 5585 Å, 5962 Å and 6385 Å belonged to one system and involved 0–0, 0–1 and 0–2 transitions respectively.