A New Band in the Spectrum of the OH Molecule

Although the ultraviolet "water vapor" bands were among the earliest molecular spectra to undergo extensive investigation, heretofore only six bands have been reported. These involve transitions between the (0, 1, 2) vibrational levels of an excited ${}_{}{}^2{}_{}{}^{}\Sigma$ state and the (0, 1) vibrational levels of the normal ${}_{}{}^2{}_{}{}^{}\Pi$ state. With improved conditions for exciting the spectrum we have obtained 91 lines, heretofore unreported, in the neighborhood of the (0′, 1″) band at $\lambda 3428$. 44 of these lines prove to be extensions of $\lambda 3428$; 54 lines (including 11 in common with $\lambda 3428$) form a new band with a head at $\lambda 3484$; and 4 lines remain unidentified. Analysis of the new band identifies it as the (1′, 2″) band of the water vapor system. Rotational constants for the normal ${}_{}{}^2{}_{}{}^{}\Pi$ electronic state of OH are: ${B_e}^{\prime \prime }=19.025\mathrm{}$, ${\alpha }^{\prime \prime }=0.724\mathrm{}$, ${D_e}^{\prime \prime }=-1.97\mathrm{}\times {10}^{-3\mathrm{}}$, ${\beta }^{\prime \prime }=5.0\mathrm{}\times {10}^{-5\mathrm{}}$, and ${r_e}^{\prime \prime }=0.964\mathrm{}\times {10}^{-8\mathrm{}}$ cm. Vibrational constants are: ${{\omega }_e}^{\prime \prime }=3734.9\mathrm{}$ and ${x_e}^{\prime \prime }{{\omega }_e}^{\prime \prime }=82.6\mathrm{}$. Rotational and vibrational constants for the excited ${}_{}{}^2{}_{}{}^{}\Sigma$ state are also evaluated and are tabulated.