We apply several techniques to the study of the B̃ 2A′′-X̃ 2A′′ band system of the jet-cooled vinoxy radical, CH2CHO. Vibronically resolved excitation spectra are obtained using both laser-induced fluorescence (LIF) and a two-color resonant four-wave mixing (TC-RFWM) scheme that provides the nonlinear equivalent of hole-burning spectra. Rotationally resolved LIF spectra recorded at low temperatures (⩽3 K) provide rotational constants for 9 B̃-state levels. We also measure the fluorescence lifetimes of 19 B̃-state levels and obtain high-quality dispersed fluorescence (DF) spectra from seven of the most strongly fluorescing levels in the B̃ state. The excitation and DF spectra reveal far more vibrational levels in the two electronic states than have been previously observed. In total, we provide assignments for 54 levels observed in the first 3650 cm−1 of the B̃ state and for 57 levels in the first 3100 cm−1 of the X̃ state. These assignments include the identification of the a′ fundamentals for ν4 through ν9 and all three a′′ overtones, 2ν10 through 2ν12, in both states. The differences between the TC-RFWM and LIF spectra and the measured lifetimes indicate a dramatic increase in the predissociation rate of the B̃ state beginning at 1190 cm−1 above the origin. The predissociation rate is markedly mode-specific and is enhanced by out-of-plane excitation, possibly due to vibronic coupling with either the Ã 2A′ or C̃ 2A′ electronic states. The congestion and complexity of the DF spectra at high energies provides direct evidence of extensive intramolecular vibrational redistribution on the ground-state potential surface.

Metal compound clusters containing niobium and carbon are produced in a laser vaporization pulsed-nozzle cluster source. The mass distributions of cations produced from this source are measured under different conditions. These cations are mass-selected in a specially designed reflectron time-of-flight mass spectrometer and photodissociated at various laser wavelengths. Mass distributions provide evidence for the preferential formation of the M8C1Z stoichiometry observed previously and associated with the "met-cars" cage structure. Additional abundant masses indicate the formation of face-centered-cubic crystallite stoichiometries. Photodissociation in both the met-cars and crystallite systems results in the formation of a broad distribution of fragment ions, with some enhancement in abundance for the smaller symmetric crystallites. This photochemistry is markedly different from that observed previously for metal-carbon clusters containing titanium, vanadium, molybdenum, or zirconium.

Articles you may be interested inCross sections for rotational decoherence of perturbed nitrogen measured via decay of laser-induced alignmentWe report the first laser-induced fluorescence ͑LIF͒ excitation spectrum of the ketenyl radical, HCCO, which is produced by the 193 nm photolysis of ketene in a free jet expansion. A series of vibronic bands in the B 2 ⌸ -X 2 AЉ system are observed. The LIF band positions and rotational structures are in excellent agreement with those of a recent photofragment yield ͑PFY͒ spectrum ͓D. L. Osborn et al., J. Chem. Phys. ͑to be published͔͒ from the origin at 33 424 cm Ϫ1 to 35 100 cm Ϫ1 . At higher energies the LIF spectrum breaks off sharply due to a rapid increase in the rate of predissociation. The lifetime of the vibrationless level of the B state is less than 1 ns; the estimated quantum yield of fluorescence is ϳ10 Ϫ3 .

Articles you may be interested inHigh-resolution spectroscopy of 4-fluorostyrene-rare gas van der Waals complexes: Results and comparison with theoretical calculations

No abstract