3546-Å System of Formaldehyde

Abstract

Bands of the ¹A″↔¹A₁ system of HCHO have been photographed in absorption at 190°K and in emission at 600°K. Twenty new bands in the absorption system are assigned. The electronic origin is discussed, and an average value of 28 193 cm⁻¹ is reported. The α₁₀ band in emission is shown to consist of two overlapping bands with origins at 27 035 and 27 025 cm⁻¹, and assignments of (0⁻00)′→(010)″ and (0⁺00)′→(100)″, respectively, are suggested. Barrier heights in the ¹A″ states of HCHO and DCDO are calculated to be 385 and 386 cm⁻¹, implying equilibrium values of 20.7° and 26.4°, respectively, for the out‐of‐plane bending angles. Some observations about the nature of the electronic transition are made.