3546-Å System of Formaldehyde

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.