화학공학소재연구정보센터
Journal of Chemical Physics, Vol.111, No.20, 9233-9241, 1999
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 mu s) 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 less than or equal to v less than or equal to 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:k(qv)(II)/10(-12) cm(3) 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 Cl-2 into the system, we observed weak emission of HCl(v), 1 less than or equal to v less than or equal to 4, upon photolysis at 193 nm. Such observation indicates that production of H, followed by reaction of H with Cl-2 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+Cl-2 are also determined. The F-elimination channel was not observed; estimated upper limit for the branching ratio is 2%.