Szu-Cherng Kuo

Rate constant and reaction channels for the reaction of atomic nitrogen with the ethyl radical

The absolute rate constant and primary reaction products have been determined at T=298 K for the atom–radical reaction N(4S)+C2H5 in a discharge flow system with collision‐free sampling to a mass spectrometer. The rate constant measurements employed low energy electron impact ionization while the product study used dispersed synchrotron radiation as the photoionization source. The rate constant was determined under pseudo‐first‐order conditions by monitoring the decay of C2H5 or C2D5 as a function of time in the presence of excess N atoms. The result is k=(1.1±0.3)×10−10 cm3 molecule−1 s−1. For the reaction product experiments using photoionization mass spectrometry, products observed at 114 nm (10.9 eV) were CD3, D2CN and C2D4 for the N+C2D5 reaction. The product identification is based on the unambiguous combination of product m/z values, the shift of the m/z peaks observed for the N+C2D5 reaction products with respect to the N+C2H5 reaction products and the photoionization threshold measured for the ma...

A discharge flow‐photoionization mass spectrometric study of HOBr(X 1A’): Photoion yield spectrum, ionization energy, and thermochemistry

The photoion yield spectrum of HOBr was measured over the wavelength range λ=108–121 nm by using a discharge flow‐photoionization mass spectrometer apparatus coupled to a synchrotron radiation source. HOBr was generated by the reaction of OH with molecular bromine. A value of (10.62±0.04) eV was obtained for the adiabatic ionization energy (I.E.) of HOBr from photoion thresholds, corresponding to the HOBr+(2A‘)←HOBr(1A’) transition. The structure observed in the spectrum is discussed in terms of the available states for HOBr+, which have been determined using multiconfiguration‐self‐consistent field calculations. A new value for ΔH0f 298(HOBr) of −9 kcal mol−1 is derived from I.E.(HOBr) and estimates of ΔHf(HOBr+).

A discharge-flow photoionization mass-spectrometric study of the BrO (X 2Π) radical. Photoionization spectrum and ionization energy

Abstract The photoionization spectrum of BrO was measured over the wavelength range λ=106–122 nm using a discharge-flow photoionization mass spectrometer apparatus coupled to a synchrotron radiation source. BrO was generated by the reaction of O( 3 P) atoms with molecular bromine. A value of 10.46±0.02 eV was obtained for the adiabatic ionization energy of BrO from photoion thresholds, corresponding to the BrO + (X 3 Σ − )←BrO(X 2 Π 3/2 ) transition. Spectra for both the 79 BrO and 81 BrO isotopes were very similar and the resultant photoion thresholds were identical, within experimental uncertainty. The structure observed in the spectra is discussed in terms of available states for BrO + , which have been calculated using MC-SCF methods.

A discharge flow-photoionization mass spectrometric study of the FO(X 2 Pi i) radical. Photoionization efficiency spectrum and ionization energy

Photoionization efficiency spectra of FO were measured over the wavelength range 80.0–100.0 nm and in the ionization threshold region, 94.0–100.0 nm, using a discharge flow-photoionization mass spectrometer apparatus coupled to a synchrotron radiation source, FO was generated by the reaction of F(2P) atoms with NO3 and via a F2/O2 discharge. A value of 12.78 ± 0.03 eV was obtained for the adiabatic ionization energy of FO from photoion thresholds which corresponds to FO+ (X 3∑−) ← FO(X 2Πi). These results, which are the first to be obtained by direct PIMS measurements, corroborate those of a photoelectron spectroscopy study; however, the ionization energy determined here is free from interferences due to other species which complicated the PES measurement. A value of 109.5 ± 8.0 kJ mol−1 for ΔfH0298(FO) is computed from the present value of IE(FO) and a previous appearance energy measurement, and a value for the proton affinity of FO is calculated to be 511.5 ± 10.0 kJ mol−1.