AAS Meeting #193 - Austin, Texas, January 1999
Session 71. Molecular Clouds
Display, Friday, January 8, 1999, 9:20am-6:30pm, Exhibit Hall 1

## [71.16] Abundances of H2, H3+ & CO in Molecular Clouds

C.A. Kulesa (Steward Observatory), J.H. Black (Onsala Space Observatory), C.K. Walker (Steward Observatory)

High-resolution infrared and submillimeter spectroscopy provides valuable insight into the physical conditions, abundances, chemistry and distribution of molecular material in interstellar clouds and star-forming regions. We have recently performed a comprehensive spectroscopic study toward obscured infrared sources in several molecular clouds (GL 490, GL 2591, NGC 2024, NGC 2264) that highlights the complementary capabilities of these techniques and provides crucial tests of theoretical models of molecular clouds. Using NOAO's high-resolution Phoenix spectrometer on the KPNO 2.1-meter telescope and the facility instrumentation at the 10-meter Heinrich Hertz Telescope (HHT) of the Submillimeter Telescope Observatory (SMTO), we have: \medskip \begin{enumerate}

\item established directly the column density of cold H2 in a sample of dense clouds where various other molecules are observed \item measured the abundance, excitation, and physical environments of 12CO and 13CO in molecular clouds with high accuracy \item observed the pivotal molecular ion H3+, allowing measurement of the cosmic-ray ionization rate (\zeta) responsible for initiating ion-molecule chemistry in dense cores of molecular clouds. These observations also constrain the formation processes of warm H2O in GL 2591 as measured by ISO. \item mapped the molecular environments of these regions in submillimeter transitions of 12CO, 13CO, C17O and C18O at high spectral resolution, allowing us to build comprehensive physical and chemical models of these clouds. \end{enumerate} Measurements of [CO/H2] vary substantially from cloud to cloud and can depart from the canonical value of 8 \times 10-5 often cited in the literature. These departures lead to improved physical and chemical models of these regions. Exciting future prospects using both high-resolution infrared spectrometers on large optical telescopes and multi-element heterodyne array receivers on large submillimeter telescopes are discussed.