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

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Electronic spectra are reported for the heteronuclear metal dimers LiCu and LiAg, with resonant one-color two-photon ionization (R2PI). The dimers are produced in a pulsed supersonic molecular beam by laser vaporization of either a copper or silver rod coated with a thin film of vacuum deposited lithium metal. A total of twelve excited electronic states for LiCu and seven for LiAg are observed. Analysis of the vibrational progressions yields ground and excited state vibrational frequencies and dissociation energies for both LiCu and LiAg. In addition, selected vibronic bands are rotationally resolved. This data, together with that obtained by Morse and co-workers for LiCu [J. Chem. Phys. (to be published)], gives bond lengths for LiCu and LiAg (r0″=2.26 and 2.41 Å, respectively). The bond lengths for LiCu and LiAg are significantly shorter than expected by comparison to the homonuclear diatomics Li2 and Cu2 or Ag2. Dissociation energies in the heteronuclear dimers are also much greater than the mean of the corresponding homonuclear dimer values. These trends indicate that ionic character plays a leading role in the ground-state bonding.

Aluminum atom van der Waals complexes of the form Al-(N2), and Al-(C02), are prepared in a molecular beam environment using a laser vaporization pulsed nozzle cluster source. These species are studied with threshold laser photoionization in a time-of-flight mass spectrometer. Ionization thresholds as a function of cluster size reveal cluster bonding energetics and evidence for intracomplex reactions. The ionization potential of A1-N2 (5.805 eV) is combined with the dissociation energy of Al+-N2 to yield the bond energy (466 cm-I) of the AI-N2 van der Waals complex. In the Al-(COz), system, the intracluster metal oxidation reaction proceeds spontaneously only after "solvation" by at least five CO:! molecules. The ionization threshold red shift indicates that Do(Al+-C02) 2 2453 cm-I.

Articles you may be interested inHigh-resolution laser spectroscopy and magnetic effect of the B ̃ 2E′ ← X ̃ 2A2′ transition of 14NO3 radicalThe electronic spectroscopy of the B 2 ⌸ -X 2 AЉ band system of the ketenyl radical, H͑D͒CCO, is investigated using laser-induced fluorescence ͑LIF͒ in a free-jet environment. Vibronically resolved excitation spectra for HCCO are obtained from 33 400 cm Ϫ1 to 35 100 cm Ϫ1 ; at higher energies the LIF spectra cutoff due to a rapid increase in the rate of predissociation. The parallel transitions from K a Љϭ1 in the ground state to the spin-orbit levels, 2 ⌸ 3/2 and 2 ⌸ 1/2 , of the origin of the B state are completely rotationally resolved for both HCCO and DCCO. Four other parallel transitions originating from K a Љϭ0 in the ground state and terminating on levels of ⌺ vibronic symmetry are observed and assigned to the two pairs of ⌺ states derived from one quantum of excitation in each of the Renner-Teller active modes, the CCO and CCH͑D͒ bend. Rotational analysis provides effective rotational constants and spin-rotation ͑orbit͒ couplings for each of these levels. In addition to the Renner-Teller and spin-orbit couplings, there is substantial evidence for additional perturbations among the low-lying bending levels in the B 2 ⌸ state of ketenyl.