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

Abstract

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(v) with 1⩽v⩽5 was observed, with intensity maxima at varied intervals after photolysis. Temporal profiles of HF(v) fit satisfactorily with a kinetic model consisting of nascent production of HF(v) followed by quenching of HF(v) by parent molecules. Measurements of rates of quenching at varied partial pressure of CH2CF2 yield bimolecular rate coefficients of quenching of HF(v) by CH2CF2:kqvII/10−12 cm3 molecule−1 s−1=1.07±0.10, 2.95±0.22, 13.5±0.9, and 45.2±4.1 for v=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 v=1–5, respectively, consistent with previous results. By adding Cl2 into the system, we observed weak emission of HCl(v), 1⩽v⩽4, upon photolysis at 193 nm. Such observation indicates that production of H, followed by reaction of H with Cl2 to form HCl(v) 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(v) 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%.