Timothy S. Zwier

The spectroscopy and single vibronic level fluorescence quantum yields of jet cooled trans‐stilbene and its van der Waals complexes

This paper reports results on the spectroscopy and dynamics of trans‐stilbene seeded in a supersonic free jet. The cooling provided by the expansion results in well‐resolved vibronic structure near the origin. Fluorescence excitation spectra reveal two low frequency vibrational modes at 82 and 95 cm−1 above the origin. By 1800 cm−1 above the origin the discrete vibronic structure has given way to a continuous absorption which extends to 6200 cm−1 blue of the origin. The fluorescence excitation spectrum is combined with a direct absorption measurement in the jet using a Xe lamp in order to obtain SVL fluorescence quantum yields for the isolated trans‐stilbene molecule. The fluorence quantum yields show no mode dependence, indicating that vibrational relaxation within the trans configuration is much faster than isomerization to the perpendicular configuration. Stilbene van der Waals complexes with helium and argon have been identified in fluorescence excitation spectra at higher nozzle backing pressures. Di...

The multiphoton ionization spectrum of complexes of benzene and acetylene

Weakly bound complexes of benzene and acetylene were formed in a supersonic molecular beam and were studied using resonantly enhanced multiphoton ionization spectroscopy. Spectral features produced by different complexes were overlapped but were resolved using a time‐of‐flight mass spectrometer detector. The 1B2u ← 1A1g transition of benzene is forbidden, but the 0–0 band of this transition was observed in the benzene–acetylene complex, the transition being weakly allowed under the lower symmetry of the complex. Features near the 610 band of benzene were observed and assigned to two different geometric isomers of the benzene–acetylene complex. Features assigned to the mixed trimer benzene–(C2H2)2 were also observed. Analysis of the rotational band contours of the benzene–acetylene origin transition indicated that in that isomer, the acetylene is located above the plane of the benzene off of the sixfold axis. Vibrational predissociation of the neutral complex was observed when one of the isomers of φ‐C2H2 ...

GROWING UP RADICAL: INVESTIGATION OF BENZYL-LIKE RADICALS WITH INCREASING CHAIN LENGTHS

Combustion processes involve complex chemistry including pathways leading to polyaromatic hydrocarbons (PAHs) from small molecule precursors. Resonance stabilized radicals (RSRs) likely play an important role in the pathways to PAHs due to their unusual stability. Benzyl radical is a prototypical RSR that is stabilized by conjugation with the phenyl ring. Earlier work on α-methyl benzyl radical showed perturbations to the spectroscopy due to a hindered methyl rotor.a If the alkyl chain is lengthened then multiple conformations become possible. This talk will discuss the jet-cooled spectroscopy of α-ethyl benzyl radical and α-propyl benzyl radical produced from the discharge of 1-phenyl propanol and 1-phenyl butanol respectively. Electronic spectra were obtained via resonant two-photon ionization, and IR spectra were obtained by resonant ion-dip infrared spectroscopy.