Cross section measurements for photodetachment or photodissociation of ions produced in gaseous mixtures of O2, CO2, and H2O

A drift tube mass spectrometer coupled with a continuous laser photon source has been used to study photodissociation of thermal energy positive ion clusters. Absolute photodissociation cross sections have been measured for O2 +(H2O)1,2, O2 +(O2), O2 +(CO2), and H+(H2O)n=1–4 at room temperature and for low field conditions (10 or 14.3×10−21 V m2). Photon wavelengths ranging from 676.4 to 454.5 nm were studied. The H+(H2O)n=1–4 were found to have small or zero cross sections; upper limits on their cross sections were obtained. The O2 +(H2O) and O2+(CO2) cross sections behave similarly over part of the photon energy range. Near 2.60 eV both ions have cross sections approaching 6×10−22 m2. The photodissociation of O2 +(CO2) produces a CO2 + photofragment. From the appearance of this fragment an upper bound on the dissociation energy of O2 +(CO2) was placed at 0.46 eV.