Nuclear Spin of H_3^+ in Diffuse Molecular Clouds

Details Nuclear Spin of H_3^+ in Diffuse Molecular Clouds Nuclear Spin of H_3^+ in Diffuse Molecular Clouds

Jun 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011mss..confetf09c&link_type=abstract

"International Symposium On Molecular Spectroscopy, 66th Meeting, Held 20-24 June, 2011 at Ohio State University. http://molspec

Astronomy and Astrophysics

Astronomy

Astronomical Species And Processes

Scientific paper

In diffuse molecular clouds (environments with high molecular fraction, but low CO abundance), the relative populations of the J=0 (para) and J=1 (ortho) rotational levels of H_2 are often used as a measure of the cloud kinetic temperature, T01. Typically, T01 is on the order of 50-70 K, but in similar environments, the excitation temperature T(H_3^+) derived from the (J,K) = (1,0) (ortho) and (1,1) (para) rotational levels of H_3^+ is 20-40 K. We have extended the number of sight lines in which both T01 and T(H_3^+) have been measured from two to five, and in four of the five cases, the two temperatures are discrepant in the same cloud. Using a steady state chemical model based on rate coefficients calculated with a microcanonical statistical approach, we find that the discrepancy between T01 and T(H_3^+) likely arises from incomplete thermalization caused by competition between the thermalization reaction H_3^+ + H_2 → H_2 + H_3^+ and dissociative recombination of H_3^+ with electrons.

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