Production of CH （A2△） by multi-photon dissociation of （CH3）2CO, CH3NO2, CH2Br2, and CHBr3 at 213 nm

In order to realize electrostatic Stark deceleration of CH radicals and study cold chemistry, the fifth harmonic of a YAG laser is used to prepare CH (A2Δ) molecules through using the multi-photon dissociation of (CH3)2CO, CH3NO2, CH2Br2, and CHBr3 at ~ 213 nm. The CH product intensity is measured by using the emission spectrum of CH (A2 Δ → X2 Π). The dependence of fluorescence intensity on laser power is studied, and the probable dissociation channels are analyzed. The relationship between the fluorescence intensity and some parameters, such as the temperature of the beam source, stagnation pressure, and the time delay between the opening of pulse valve and the photolysis laser, are also studied. The influence of three different carrier gases on CH signal intensity is investigated. The vibrational and rotational temperatures of the CH (A2 Δ) product are obtained by comparing experimental data with the simulated ones from the LIFBASE program.