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

Abstract

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.