Observations of H3+ in Dense Molecular Clouds

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Abstract
H+3 has been detected using infrared absorption spectroscopy along the lines of sight to six infrared sources in dense molecular clouds: AFGL 2136, W33A, Mon R2 IRS 3, AFGL 961E, AFGL 2591, and AFGL 490. Upper limits to the column densities of H+3 are reported for an additional nine sources. The column densities of CO toward Mon R2 IRS 3 and AFGL 961E have been determined from observations of the first-overtone lines of CO. For the six sources toward which H+3 was detected, a simple model of H+3 chemistry has been used together with column densities of H2 derived from infrared CO measurements to estimate column lengths, mean number densities, and temperatures of molecular clouds. The derived column lengths are on the order of a parsec, the number densities are 104-105 cm-3, and the temperatures are ~25-50 K.