On the deuteration of CH in dense interstellar clouds via the reaction CH + HD CHD⁺ + H

¹ LETMEX, Université de Nice Sophia Antipolis, Parc Valrose, UFR Sciences, 06108 Nice Cedex 2, France
² Departments of Physics and Astronomy, The Ohio State University, Columbus, OH 43210, USA

Corresponding author: E. Herbst, herbst@mps.ohio-state.edu

Received: 16 March 2001
Accepted: 6 July 2001

Abstract

Although deuterium isotope fractionation in cold, dark interstellar clouds is reasonably well understood via gas-phase chemistry, there are some discrepancies between observation and theory. For example, the observed abundance ratio between the deuterated species C₃HD and the cyclic molecule C₃H₂ is significantly higher than most theoretical values unless the exchange reaction C₃H + HD C₃H₂D⁺ + H₂ is efficient. In this paper, we report quantum chemical and dynamical calculations on this reaction, which show it to possess a large activation energy barrier and to be very slow at all normal interstellar temperatures.