Study of Benzene Fragmentation, Isomerization, and Growth Using Microwave Spectroscopy

Using a combination of broadband and cavity Fourier transform microwave spectroscopies, and newly developed analysis and assignment tools, the discharge products of benzene have been extensively studied in the 2-18 GHz frequency range. More than 450 spectral features with intensities greater than 6σ of the noise RMS were identified, of which of roughly four-fifths (82%) constituting 90% of the total spectral intensity were assigned to 38 species previously detected in the radio band, and nine entirely new hydrocarbon molecules were identified. The new species include both branched and chain fragments of benzene, high energy C₆H₆ isomers, and larger molecules such as phenyldiacetylene and isomers of fulvenallene; taken together they account for roughly half of the number of observed transitions and 51% of the spectral line intensity. Transitions from vibrationally excited states of several molecules were also identified in the course of this investigation. A key aspect of the present analysis was implementation of a rapid and efficient workflow to assign spectral features from known molecules and to identify line progressions by pattern recognition techniques.