# Negative Ion Formation by the Thermal Surface Ionization of Oxygen-Bearing Gases (O2, CO2, CO, NO, and NO2)

## TL;DR

This study explores how different oxygen-bearing gases form negative oxygen ions at high temperatures, revealing distinct mechanisms for each gas.

## Contribution

The paper identifies optimal temperatures and unique ion formation pathways for various oxygen-bearing gases.

## Key findings

- Optimum temperatures for O− formation range from 1548 to 1721 °C for different gases.
- NO2 likely forms O− through a two-step dissociation mechanism.
- CO forms O− primarily via electron capture followed by dissociation.

## Abstract

The formation of the oxygen negative ion O− from simple molecules such as O2, CO2, CO, NO, and NO2 is of fundamental importance in environmental, atmospheric, and biological processes. This study investigates the mechanisms of O− ion generation from these gases by analyzing the dependence of O− ion current intensity on filament temperature. Optimum temperatures for O− formation were identified for each gas, ranging from 1548 to 1721 °C. A comparison with the calculated thermal decomposition temperatures of the respective compounds indicates that distinct ion formation pathways are involved. For NO2, the process likely involves a two-step dissociation mechanism, with molecular oxygen (O2) formed in the first step, subsequently dissociating into O− and O atoms. In contrast, for CO, O− formation predominantly occurs through electron capture followed by molecular dissociation. These findings underscore the complex nature of negative surface ionization, which includes contributions from the capture of emitted from the cathode electrons by molecules.