DIODE LASER STARK AND HETERODYNE SPECTROSCOPY OF $CH_{3}OH$

Author Institution: U.S. Army Electronics Research and Development Command, Harry Diamond LaboratoriesThe high resolution attainable with lead-salt diode lasers has permitted simple extension into the mid-infrared region of two techniques routinely used in microwave absorption spectroscopy. Stark effect analysis and heterodyning. These two techniques have facilitated the assignments of transitions and accurate measurements of absorption frequencies. These techniques will be illustrated with results obtained near $9.6\;\mu m$ for $D_{2}O, CH_{3}F CH_{3}OH$, with emphasis on the latter. For $CH_{3}OH$, lines in the simpler P and R branch multiplets of the C-O stretch mode were identified by direct observation in absorption of the linear and quadratic Stark patterns produced when static electric fields were applied to the gas with $\stackrel{\rightarrow}{E}$ parallel or perpendicular to the linear polarization of the diode laser radiation. Multiplets have been identified extending from the R(11) near $1052\;cm^{-1}$ through the Q branch to the P(10) near $1017\;cm^{-1}$. Assignments of the quantum numbers n, J, $\tau$, and K for certain lines in the P(J) and R(J) multiplets have beer made possible because of the constant width of the multiplets, the similarity of the structures of adjacent multiplets, and our Stark measurements. In addition, a line-tunable $CO_{2}$ laser was used to heterodyne against the diode laser radiation and establish the positions of well-known $CO_{2}$ laser frequencies in the $CH_{3}OH$ spectrum. The application of these results to optically pumped submillimeter wave lasers will be discussed