Visible and near infrared emission spectra of PCl excited in the reaction of Ar(3P2, 0) with PCl3: Vibrational analysis of PCl A3Π → X3Σ− and b1Σ+ → X3Σ−

Two band systems of PCl, A³Π_r → X³Σ^? and b¹Σ⁺ → X³Σ^?, have been observed from the reaction of $\text{Ar}\text{(}{}^3\text{P}{}_{\mathrm{2,\; 0}}\text{)}$ with PCl₃ at pressures of 1–2 Torr. Seventy-eight bands of P³⁵Cl and 31 bands of P³⁷Cl in the region 4000–6000 Å have been assigned to the A³Π_r → X³Σ^? system and include levels with v′ = 0, 1, 2 and v″ = 3–18. The ground state numbering was obtained from a study of the vibrational isotope effect. The (0,0) sequence of the b¹Σ⁺ → X³Σ^? system occurs near 8200 Å and has been observed up to v′ = 10. Vibrational constants for all three states are derived from least-squares fits of the measured bandhead wavenumbers. The A ← X absorption system of PCl reported by Basco and Yee in flash photolysis of PCl₃ was not observed, and is probably due to absorption to a Rydberg state of PCl.