Knowledge Bank

Laser photoacoustic spectra of RDX, TNT, heroin, morphine and narcotine in the powder form and of methanol, ethanol and trichloroethylene in the varpor phase have been recorded in the 9.6 and $10.6\mu$ m regions using a rotational line tunable $CO2$ Iser. The persistent vibrational bands in RDX are observed at $1045,941cm-1$ and those in TNT are at $978,946cm-1$. The characterstic bands in heroin are at $976,944cm-1$, in morphine at $973,949cm-1$ and in the narcotine at 1043, 936 and $929cm-1$. Assignments of the vibrational bands in terms of normal modes have been made with the help of ab initio calculations of molecular geometries and the intramolecular force constants. In the case of vapor phase spectra, the rotational contours with two prominent peaks in methanol and ethanol are observed in the $9.6\mu$ m region whereas trichloroethylene exhibits three peaks in its rotational contour in the $10.6\mu$ m region.