The C(3P) + NH3 reaction in interstellar chemistry: II. Low temperature rate constants and modeling of NH, NH2 and NH3 abundances in dense interstellar clouds

TL;DR

This study measures the rate constants of the C + NH3 reaction at low temperatures relevant to interstellar space and models its impact on nitrogen hydride abundances in dense clouds.

Contribution

It provides the first low-temperature rate constants for the C + NH3 reaction and assesses its significance in astrochemical models.

Findings

Reaction rate increases at lower temperatures, reaching 1.8×10⁻¹⁰ cm³ molecule⁻¹ s⁻¹ at 50 K.

The C + NH3 reaction significantly influences nitrogen hydride abundances in dense interstellar clouds.

The ortho-to-para ratio of H₂ affects NH₃ formation in the modeled environments.

Abstract

A continuous supersonic flow reactor has been used to measure rate constants for the C + NH3 reaction over the temperature range 50 to 296 K. C atoms were created by the pulsed laser photolysis of CBr4. The kinetics of the title reaction were followed directly by vacuum ultra-violet laser induced fluorescence (VUV LIF) of C loss and through H formation. The experiments show unambiguously that the reaction is rapid at 296 K, becoming faster at lower temperatures, reaching a value of 1.8 10-10 cm3 molecule-1 s-1 at 50 K. As this reaction is not currently included in astrochemical networks, its influence on interstellar nitrogen hydride abundances is tested through a dense cloud model including gas-grain interactions. In particular, the effect of the ortho-to-para ratio of H2 which plays a crucial role in interstellar NH3 synthesis is examined.