Roger. Tembreull

Free-jet spectra and structure of o-, m- and p-dihydroxybenzenes

Abstract Analysis of the free-jet spectra of hydroquinone (para), catechol (ortho) and resorcinol (meta) shows the presence of multiple origins in each molecular spectrum which are interpreted as belonging to separate structural isomers.

Excited state spectroscopy of para di-substituted benzenes in a supersonic beam using resonant two photon ionization

Abstract Excited state vibronic spectra of p -aminophenol, p -cresol, p -fluoroaniline, p -fluorophenol, hydroquinone and p -toluidine have been obtained using resonant two photon ionization supersonic beam mass spectrometry. Despite marked similarities in the spectra, notable differences exist and different para polyatomic substituents in the same molecule show vibronic evidence of their real molecular symmetry of C 2ν . Expansion of the ring is also noted upon excitation in all cases. Further, it is now evident that the assignment of some vibronic bands historically interpreted as sequence structure must be reconsidered since molecules like hydroquinone are mixtures of cis and trans and others have a vibronic structure arising from the polyatomic nature of the substituents ( c ƒ. CH 3 ).

RESONANT TWO-PHOTON IONIZATION IN BIOMOLECULES USING LASER DESORPTION IN SUPERSONIC BEAM-MASS SPECTROMETRY.

Resonant two-photon ionization (R2PI) has been demonstrated for several classes of biomolecules in a supersonic jet. These thermally labile and nonvolatile species have been vaporized with pulsed laser desorption, with the use of a CO2 laser from a ceramic surface with subsequent entrapment in a jet expansion. R2PI is then demonstrated in a time-of-flight mass spectrometer (TOFMS) with the use of ultraviolet laser radiation at either 280 or 266 nm. The 280-nm wavelength is found to be a fairly general tool for exciting the π-π* transition of the molecules under study, viz., metabolites of catecholamines, indoleamines, and tyrosine near their respective origin regions. The resulting mass spectra exhibit soft ionization where either molecular ions or minimal fragmentation is produced. At frequencies of much higher energy than that of the origin, fragmentation becomes increasingly difficult to prevent.

A System for Pulsed Laser Desorption of Small Biomolecules With Supersonic Jet Injection Using Resonant Two-Photon Ionization (R2Pi) Detection

ABSTRACT A system is described that uses laser desorption as a means of volatilizing small, thermally-labile biomolecules into the gas phase as neutral species. The desorbed molecules are then entrapped in a pulsed supersonic jet expansion of CO2 and swept into a differentially pumped time-of-flight mass spectrometer. Laser induced R2PI at 280 nm or 266 nm through the π-π* transition is used to ionize these species softly at modest input energy.