Knowledge Bank

“The absorption spectrum of $H2CO$ vapor show a weak system of bands between 3600$\backslash AA$ and 4260$\backslash AA$. Absorption paths varying from 5 to 120 meter-atmospheres reveal nine bands in this region which have envelopes distinctly different from those of the well known 3530$\backslash AA$ system. Each band appears double, having two absorption maxima of about equal peak intensity. Four of these bands have been previously $reported1,2,3$. A band at $25243cm-1$ is probably the (0.0) band of this system. Four much weaker bands lying to the red side of the origin are regarded as temperature sensitive. Two of these bands involve the frequency $v\_\{2\}^\{\backslash prime\}^\{\backslash prime\}=\; 1746$ $cm-1$ of the ground state. An excited state interval of $1183cm-1$ is interpreted as $v2\prime$. The principle problem of the analysis is the interpretation of an interval of $535cm-1$ between the (0.0) band and its nearest neighbor toward the violet. This interval can be explained in terms of an inversion in the nonplanar bending mode of the excited state. The results are: ($1+-)+$) $535cm-1$, ($0-0+$) $29cm-1$, ($1--1+$) $240cm-1$. The latter two intervals are based on the assumption that two of the temperature sensitive bands involve the nonplanar bending mode of the ground state.”