Analysis of the 2973-Å Absorption System of Phosgene

Abstract

The near-ultraviolet absorption of phosgene has been assigned to a π* ← n, 1A2 ← 1A1, electronic transition from vapor-phase spectra recorded under conditions of high resolution and low temperature. Progressions in ν1′, ν2′, ν3′, ν4′, and ν4″ have been identified in the spectrum and have been analyzed in terms of vibronic transitions between a planar ground and a nonplanar excited state. A barrier height of 3170 cm−1 and a nonplanar equilibrium angle of 32.5° were calculated for the upper state from a fit of the energy levels of a Lorentzian–quadratic potential function to the observed levels of ν4. The false origin, 401, of the spectrum has been assigned to the band at 33 631 cm−1. An oscillator strength of f = 1.04 × 10−3 has been obtained for the A21 ← A11 transition.