THE 3960$\AA$ ABSORPTION SYSTEM OF $H_{2}CO^{*}$

$^{*}$Supported by the Air Force Office of Scientific Research of the ARDC. $^{1}$E. S. Ebers. PhD Thesis, Harvard University (1935). $^{2}$A. D. Cohen and C. Reid, J. Chem. Phys. 24, 85 (1956). $^{3}$G. W. Robinson, Can. J. Phys. 34, 699 (1956).Author Institution: A and M College of Texas“The absorption spectrum of $H_{2}CO$ vapor show a weak system of bands between 3600$\AA$ and 4260$\AA$. 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$\AA$ system. Each band appears double, having two absorption maxima of about equal peak intensity. Four of these bands have been previously $reported^{1,2,3}$. A band at $25243 cm^{-1}$ 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 $v_{2}^{\prime}^{\prime}= 1746$ $cm^{-1}$ of the ground state. An excited state interval of $1183 cm^{-1}$ is interpreted as $v_{2}^{\prime}$. The principle problem of the analysis is the interpretation of an interval of $535 cm^{-1}$ 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: ($1^{+}-)^{+}$) $535 cm^{-1}$, ($0-0^{+}$) $29 cm^{-1}$, ($1^{-}-1^{+}$) $240 cm^{-1}$. 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.