Photodissociation of 1,1-difluoroethene (CH₂CF₂) at 193 nm monitored with step-scan time-resolved Fourier-transform infrared emission spectroscopy

We measured time-resolved vibration-rotational emission of HF (Hartree-Fock) at various intervals (5-500 μs) after photolysis of 1,1-difluoroethene (CH₂CF₂) at 298 K with an excimer laser at 193 nm by means of a step-scan Fourier-transform spectrometer. Emission of HF(ν) with 1 ≤ ν ≤ 5 was observed, with intensity maxima at varied intervals after photolysis. Temporal profiles of HF(ν) fit satisfactorily with a kinetic model consisting of nascent production of HF(ν) followed by quenching of HF(ν) by parent molecules. Measurements of rates of quenching at varied partial pressure of CH₂CF₂ yield bimolecular rate coefficients of quenching of HF(ν) by CH₂CF₂:k^II_qν/10 ^-12cm³molecule^-1 s^-1 = 1.07±0.10, 2.95±0.22, 13.5±0.9, and 45.2±4.1 for ν = 1-4; listed errors represent one standard deviation. The nascent vibrational distribution of HF is (0.365±0.014):(0.255±0.017):(0.177±0.015):(0.134±0. 014):(0.069±0.012) for ν =1-5, respectively, consistent with previous results. By adding Cl₂ into the system, we observed weak emission of HCl(ν), 1≤ν≤4, upon photolysis at 193 nm. Such observation indicates that production of H, followed by reaction of H with Cl₂ to form HCl(ν) takes place as a minor channel. Incorporation of this H-elimination channel into the kinetic model yields a branching ratio of 0.10±0.03 relative to the HF-elimination channel. Bimolecular rate coefficients of quenching of HCl(ν) by CH₂CF₂ and vibrational distribution of HCl from the reaction H+Cl₂ are also determined. The F-elimination channel was not observed; estimated upper limit for the branching ratio is 2%.