Infrared-induced reaction of Cl atoms trapped in solid parahydrogen

Abstract

The 355 nm photodissociation of Cl₂ trapped in a solid parahydrogen matrix at 2 K leads to the formation of isolated Cl photofragments. At these low temperatures (k_BT ≈ 1.4 cm⁻¹), the Cl atoms can not react with the parahydrogen matrix since the reaction Cl + H₂(v = 0, j = 0) → HCl(v = 0, j = 0) + H is endothermic by 360 cm⁻¹. Irradiation of the Cl atom doped parahydrogen solid with broadband infrared radiation from 4000 cm⁻¹ to 5000 cm⁻¹ induces reaction of atomic Cl with the parahydrogen matrix to form HCl. The infrared-induced chemistry is attributed to solid parahydrogen absorptions that lead to the creation of vibrationally excited H₂(v = 1), which supply the necessary energy to induce reaction. The kinetics of this low temperature infrared-induced reaction is studied using Fourier Transform infrared spectroscopy of the HCl reaction product. The HCl formation kinetics is first-order and the magnitude of the effective rate constant for the infrared-induced reaction depends on the properties of the near infrared radiation.