Photodissociation of CH3Cl+ and CH3Br+ in a tandem quadrupole mass spectrometer

A new tandem quadrupole photodissociation mass spectrometer was used to measure photodissociation cross sections for the reactions, CH₃Cl⁺ → CH₃⁺ + Cl and CH₃Br⁺ → CH₃⁺ + Br in the gas phase using wavelength-selected light. The results on CH₃Cl⁺ are compared with the earlier work of Dunbar. For both reactions we are able to observe photodissociations occurring with small cross sections (≈ 2 × 10^?20 cm²) in the visible region near the thermochemical thresholds.