Hot H Atoms in Gas Phase Photochemistry

Abstract

By photolyzing hydrogenated molecules, H or D atoms with kinetic energies in the range of about o.sre 5 eV are produced. The special features of their chemical properties are reviewed and compared with recoil tritium atom reactions on the one hand and with systems in thermal equilibrium 011 the other. Although the mechanism of reactive and non-reactive collisions are by no means well known. hot hydrogen atom chemistry is, in first approximation, rather similar to high temperature chemistry. Howe ve r , energy losses by energy transfer to molecules and even to rare gases are much smaller than expected from classical hard-sphere models. For the sake of clearness, this article is rather arbitrarily, divided into three parts: physical aspects. various modes of formation and chemical properties.

IN MY TIME: Scenes of Scientific Life

“…The theme of VUV photochemistry of gases was further developed in France over several years in studies by Catherine Vermeil and her coworkers (145), who remained in Paris after we had left for Orsay.…”

Reactions of photochemically produced hydrogen atoms at energies below 1.8 electron volts

“…Since then much research effort has been expended to gain insight into the factors determining the reactivity of hot hydrogen atoms, and this work has been carefully reviewed by Vermeil.4 This laboratory contributed a study of the flash photolysis of hydrogen iodide in the presence of C2D6, C3D8, n-CjDio, and various C2-D6_"H" ethanes. 6 Whereas the hot hydrogen atoms produced photochemically were below 4 eV in energy, the hot hydrogen atoms produced by nuclear recoil were in the 192,000-eV region. These higher energy H atoms were the subject of intensive studies by the late Wolfgang6 and Rowland,7 who have written comprehensive reviews.…”

“…In contrast, recoil species produced by the 870( , )-38C1, 19F(n,2n)18F, or 3He(n,p)T nuclear reactions react as neutral atoms and in low or ground electronic states. [4][5][6] (1) This research was supported through an Atomic Energy Commission Contract No. AT(11-1)-1617.…”