Matrix isolation study of electron impact on H2O. Infrared spectrum of OH− in solid argon

Abstract

A thermionic electron source capable of delivering 10–200 mA of electrons at low energies (30–200 eV) has been mated to a matrix isolation apparatus and employed to study electron impact on water. Three products were trapped in the argon matrix; OH radical (3452.7, 3478.1 cm−1), ArnH+ (903.7 cm−1), and a new species absorbing at 3548.9 cm−1 with a 3554.0 cm−1 shoulder. The latter is identified as OH− owing to diatomic D and 18O isotopic shifts and agreement with recent gas phase work. The 3548.9 cm−1 absorption is assigned to the R(0) vibration–rotation band of OH−, which is red shifted 42.6 cm−1 by the argon matrix. This shift is slightly more than the 38.4 cm−1 matrix shift for the R(0) line of HF. Product band intensities showed no dependence on electron energy above 30 eV but showed a nonlinear dependence on electron current, which suggests that OH is produced by primary electron impact on water and that OH− and ArH+ solvated by argon are produced by secondary processes.