On microwave discharge sources of new chemical species for matrix-isolation spectroscopy and the identification of charged species

Abstract

The mechanism for trapping new chemical species by condensing the products of a microwave discharge with inert matrices has been investigated. Variation of geometrical, electrical, and chemical parameters of the Ar, HCl, Cl₂ system indicated that the major product species—HCl₂ radical or anion—was formed under conditions where neither ions nor atomic species produced in the discharge were condensed in the matrix. The mechanism for forming the product species is vacuum ultraviolet photolysis of the sample during deposition with radiation from the microwave discharge, since a coaxial orifice discharge tube provided photolysis and produced the product species, while studies with an off‐axis orifice discharge tube, which could not serve as a photolysis source, did not produce the product. The H atom–Cl₂ reaction gave HCl using both discharge tubes, but the HCl^x₂ species was produced only with the coaxial tube. Hence, this species requires vacuum ultraviolet light in addition to H and Cl atoms for its production, and its identification as HCl⁻₂ is strongly supported. Similar observations of Ar_nD⁺ and O⁻₃ with the coaxial tube, but not with the off‐axis tube, confirm their identification as charged species.