Mid-Infrared Diode Laser Spectroscopy of X̃¹A′ HC³⁵Cl

The observation of the C-Cl stretching fundamental of HC³⁵Cl in its ground X̃ ¹A′' state is reported. HCCl was formed in a continuous flow system by the excimer laser photolysis of CHBr₂Cl at 193 nm and the transient absorption recorded by infrared diode laser spectroscopy. The band has a-type character and the fundamental vibrational frequency is found to be 811.5963 cm^-1. No evidence was found for perturbations in either the ground or vibrationally excited states, implying that the excited triplet ̃³A″ states lies above the C-Cl stretching level in HCCl. The observed rotation-vibration transitions were well fit by a standard asymmetric rotor Hamiltonian. There is a decrease in the A rotational constant on vibrational excitation, suggesting that some bend-C-Cl stretch coupling is present.