Analysis of the 2973-Å Absorption System of Phosgene

The near‐ultraviolet absorption of phosgene has been assigned to a ${\mathrm{\pi *\hspace{0.17em}\leftarrow \hspace{0.17em}n,}}^1{A}_2{\mathrm{\hspace{0.17em}\leftarrow \hspace{0.17em}}}^1{A}_1$ , electronic transition from vapor‐phase spectra recorded under conditions of high resolution and low temperature. Progressions in ${\nu }_1{\mathrm{\prime ,\; \nu }}_2{\mathrm{\prime ,\; \nu }}_3{\mathrm{\prime ,\; \nu }}_4\mathrm{\prime ,}\mathrm{and}{\nu }_4″$ 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 ${\nu }_4$ . The false origin, 4₀¹, of the spectrum has been assigned to the band at 33 631 cm⁻¹. An oscillator strength of ${\text{f\hspace{0.17em}=\hspace{0.17em}1.04\hspace{0.17em}×\hspace{0.17em}10}}^{\text{−3}}$ has been obtained for the ${}^1{A}_2{\mathrm{\hspace{0.17em}\leftarrow \hspace{0.17em}}}^1{A}_1$ transition.