Ionization efficiencies of C3H6, C4H8, C6H12, C2H6O,and C3H8O isomers

Ionization efficiencies of 14 organic compounds have been measured in the wavelength region from 105 to 134nm using an ionization chamber. The compounds examined are cyclopropane, propylene, l-butene, isobutene, cis-and trans-2-butenes, cyclohexane, 1-hexane, tetramethylethylene, ethyl alcohol, dimethyl ether, n-, and iso-propyl alcohol, and ethyl methyl ether. The ionization efficiencies of cyclopropane and cyclohexane monotonically increase with increasing photon energy, but those for the others show a peak or a shoulder in the wavelength region of the present work.     

Isomer energy differences for the C4H3 and C4H5 isomers using diffusion Monte Carlo

A new diffusion Monte Carlo study is performed on the isomers of C4H3 and C4H5 emulating the methodology of a previous study (Int. J. Chem. Kinet. 2001, 33, 808). Using the same trial wave function form of the previous study, substantially different isomerization energies were found owing to the use of larger walker populations in the present work. The energy differences between the E and i isomers of C4H3 were found to be 10.5 +/- 0.5 kcal/mol and for C4H5, 9.7 +/- 0.6 kcal/mol. These results are in reasonable accord with recent MRCI and CCSD(T) findings.     

Neutralization-reionization study of C6H6O isomers

Neutralization-reionization (⁺NR⁺) mass spectrometry is employed to examine the behavior of C₆H₆O isomers in the gas phase. Phenol and cyclohexa-2,4-dienone are found not to interconvert following neutralization with mercury of their corresponding cation radicals at 9.9 keV kinetic energy. A very low extent of isomerization is observed following collisional activation of fast C₆H₆O neutrals with helium. The ⁺NR⁺ and collisionally activated dissociation spectra, the latter obtained at unit mass resolution, are used to identify these [C₆H₆O]^{+ ˙} isomers. Hexa-1,3,5-trienal is found to cyclize spontaneously to cyclohexa-2,4-dienone during attempted pyrolytic preparation. The thermochemistry of these C₆H₆O molecules and cation radicals is discussed on the basis of experimental data and MNDO calculations.