Unusual Quartet-Doublet Phosphorescence from the Phosphaethynyl Radical, CP

We report the first detection of phosphorescence from the phosphaethynyl radical. This rare instance of quartet-doublet emission, studied here in solid argon, is presumably promoted by efficient intersystem crossing from the originally photoexcited doublet (B² Σ⁺ ) to the adjacent second quartet state, 1⁴ Δ. Vibronic progressions were traced for the a⁴ Σ⁺ -X² Σ⁺ and a⁴ Σ⁺ -A² П_i systems from their origins up to (v'=0)→(v''=5) and (v'=0)→(v''=2) bands, respectively. The measured phosphorescence lifetime is 108 ± 3 ms.