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In this work, we present an experimental study of dissociative excitation of CH 4 utilizing a crossed electron molecular beam experiment. Methane was excited by nearly monochromatic electrons generated by a trochoidal electron monochromator. The dissociative products were identified on the basis of the emission spectra in the ultraviolet-visible (UV/VIS) spectral range. The excitation functions were recorded as the function of the electron energy for different emission bands of the fragments (Balmer series for H: n = 3,4 . . . 9→2, and moreover, CH: A 2 →X 2 , CH: B S 0 ). From the experimental data we have determined the threshold energies for excitation of particular fragments. Present experimental results indicate that the threshold energies for some dissociative excitation channels could be lower by ∼1-2 eV in comparison to earlier studies and indicate that different dissociative processes may be operative at the threshold than assumed in the former studies.

The optical emission spectrum of acetylene excited by monoenergetic electrons was studied in the range 190-660 nm. The dissociative excitation and dissociative ionisation associated with excitation of the ions initiated by electron impact were dominant processes contributing to the spectrum. The spectrum was dominated by the atomic lines (hydrogen Balmer series, carbon) and molecular bands (CH(A-X), CH(B-X), CH + (B-A), and C2).Besides the discrete transitions we have detected the continuum emission radiation of ethynyl radical C2H(A-X). For most important lines and bands of the spectrum we have measured absolute excitation-emission cross sections and determined the energy thresholds of the particular dissociative channels.

2,4,6-trichloroanisole and 2,4,6-tribromoanisole were investigated by means of electron transmission spectroscopy and two different types of dissociative electron attachment spectrometers. The results obtained were interpreted with the support of density functional theory calculations. The dominant dissociative decay channels of the temporary molecular negative ions lead to the formation of Cl and Br in the low electron energy region. Formation of long-lived parent anions is observed at thermal electron energies. Their relative intensity depends on the experimental time window, ∼36 μs in the case of the static magnet mass analyzer and ∼200 μs for the quadrupole mass analyzer employed. The results obtained may be useful for rapid detection of these compounds in wine and pharmaceutical industries, as well as other branches connected to the food industry, e.g., packaging.