| A method for the production and noble gas matrix-isolation of cyclic and polycyclic aromatic hydrocarbon radicals was desired as an alternative to traditional photolysis and vacuum pyrolysis methods. In particular, a method was sought which would; (a) generate hydrocarbon radicals in high enough concentrations for detection by Fourier transform infrared absorption spectroscopy, and (b) effectively avoid secondary reactions. If the method could also be combined with other detection techniques such as mass spectrometry this would be advantageous.; Two identical hyperthermal, pulsed nozzle sources were designed and successfully constructed for the generation of short-lived, reactive species by flash pyrolysis of stable precursors in a stream of noble gas. One nozzle was interfaced with a photo-ionization, reflectron, time-of-flight mass spectrometer, the other with a matrix isolation cryostat chamber for dosing directly onto a cold matrix substrate.; Three prototypical cyclic hydrocarbon radicals, phenyl (C6H 5), phenoxy (C6H5O), and cyclopentadienyl (C 5H5) radical were produced and detected in time-of-flight mass spectrometry. Subsequently, the radicals were produced and trapped in argon matrices at 10 Kelvin and their infrared absorption studied by Fourier transform spectroscopy.; The phenyl radical was successfully produced from the flash pyrolysis of iodobenzene in a hyperthermal pulsed nozzle. The optimal pyrolysis temperature was monitored by time-of-flight mass spectrometry and, subsequently, the radical was trapped in an Ar matrix at 10 K The FTIR spectrum of the matrix isolated radical was measured in the mid-infrared, 400--4000 cm-1 , and all but one mode (nu14) were observed. The results were used as a complementary data set in a thorough reassignment of earlier reported IR spectra of the phenyl radical. Taking the gas-to-matrix shifts into account, as well as matrix inhomogeneous line broadening, the vibrational frequencies reported are within +/-1% error of unperturbed gas-phase values.; A comparison between the normal modes of C6H5 and the diradical o-C6H4 to those in C 6H6, using displacement coordinates from DFT harmonic frequencies, allowed for a correlation of the normal modes, which was used to construct energy level diagrams, correlating experimental vibrational energy levels of C6H6 to C6H5, and C6H 6 to o-C6H4. The results suggest that vibrational spectra of C6H6 and C6H 5 or o-C6H4 are simply related.; The phenoxy radical and its fully deuterated isotopomer were produced from flash pyrolysis of methoxybenzene (anisole) and methoxybenzene- d8, respectively, and the IR spectra of the radicals trapped in Ar matrices were reported for the first time. Both the production and spectroscopy of C5H5 and C5D5 posed an experimental challenge and preliminary results are reported. C5H5 was produced from three different precursors and consistency between the measured FTIR spectra in the 400--1,500 cm-1 spectral range was observed. |
