Infrared-emissivity of HD in MHD-shocks

A discussion of IR-line emission of deuterated hydrogen HD that emanates from regions of shocked molecular gas (C-type) is presented. Results are given for shock speeds of 15<u_s<45 km s"-"1 and pre-shock densities of 10"4<n_H<10"6 cm"-"3 where all available data for HD to date are utilized. We find that a fraction of HD is converted to atomic deuterium in the hot post-shocked gas with u_s>or#approx#30 km s"-"1 when H_2 becomes sufficiently dissociated. However, a part of this atomic deuterium is recovered to HD through chemical reactions with H_2 when the shocked gas cools down again. Measurements of HD line intensities may be used to derive its abundance in the dense interstellar medium (ISM). Having assumed a deuterium abundance of HD/H_2=3.0x10"-"5 for the ISM we find that line emission of HD may be detectable with currently available IR-spectrometers at ground based telescopes when the pre-shock densities are n_H>or#approx#10"5 cm"-"3. ISO may even observe rotational transitions of HD from less dense gas. (orig.)Available from TIB Hannover: RN 9303(322) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman