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

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), Ar/sub n/H+ (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