Knowledge Bank

Bands of the $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}A\prime \prime \to 1A1$ system of HCHO have been photographed in absorption at $190\circ K$ and in emission at $600\circ K$. Twenty new bands in the absorption system are assigned. The electronic origin is discussed, and an average value of $28,193cm-1$ is reported. The $\alpha 10$ band in emission is shown to consist of two overlapping bands with origins at 27,035 and $27,025cm-1$, and assignments of $(0-00)1\to (010)\prime \prime$ and $(0+00)1\to (100)\prime \prime$, respectively are suggested. Barrier heights in the $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}A\prime \prime$ states of HCHO and DCDO are calculated to be $385cm-1$ and $386cm,-1$ implying equilibrium values of $20.7\circ$ and $26.4\circ$, respectively, for the out-of-plane bending angles. Some observations about the nature of the electronic transition are made.