Articles you may be interested inThe unimolecular dissociation of HCO. II. Comparison of calculated resonance energies and widths with high resolution spectroscopic data Theoretical stabilization and scattering studies of resonances in the addition reaction H+CO = HCO J. Chem. Phys. 94, 4192 (1991); 10.1063/1.460652Collision energy dependence of Penning ionization electron spectra in crossed supersonic beams: He*(21S)+N2We use dispersed fluorescence ͑DF͒ and stimulated emission pumping ͑SEP͒ spectroscopies on the B 2 AЈ -X 2 AЈ system of jet-cooled HCO to measure the vibrational energies, resonance widths, and relative fluorescence intensities of 73 bound and resonance states supported by the ground-state potential energy surface. The SEP experiments use both two-color resonant four-wave mixing ͑RFWM-SEP͒ and the more conventional technique in which SEP signals are obtained from fluorescence depletion ͑FD-SEP͒. Where applicable, RFWM-SEP provides superior spectra to those obtained with FD-SEP, which is susceptible to saturation broadening that can prevent accurate determinations of resonance widths. The observed bound and resonance states span an energy range of 2000-21 000 cm Ϫ1 and comprise a wide range of vibrational excitation among the three vibrational modes, including states with 1-12 quanta of excitation in the C-O stretch, 0-5 quanta of bending excitation, and 0-1 quanta of excitation in the C-H stretch. The widths are markedly mode-specific and often display striking, nonmonotonic variations with increasing C-O stretch excitation. We compare our results to those of previous DF and SEP studies and to recent dynamical calculations of resonance energies and widths that use realistic potential surfaces derived from ab initio calculations. The resonance widths are particularly sensitive gauges of the unimolecular dissociation dynamics and provide stringent tests of theoretical potential surfaces.

A model calculation for nonimpact four wave mixing AIP Conf. Proc. 216, 323 (1990); 10.1063/1.39930Field and pressure induced fourwave mixing line shapes AIP Conf. Proc. 172, 249 (1988); 10.1063/1.37365Fourwave mixing spectroscopy of state selective collisions in gases and solids AIP Conf.We present a combined theoretical and experimental study of the application of two-color resonant four-wave mixing ͑RFWM͒ to stimulated emission pumping ͑SEP͒ spectroscopy. The theoretical approach employs time-independent, diagrammatic perturbation theory and a spherical tensor analysis in an extension of a recent treatment of degenerate four-wave mixing ͓Williams, Zare, and Rahn, J. Chem. Phys. 101, 1072 ͑1994͔͒. The resulting signal expression for two-color RFWM separates the molecular properties from purely laboratory-frame factors determined by the polarizations of the input beams and the rotational branch types of the SEP PUMP and DUMP transitions. This expression is valid in the limit of weak fields and for molecules in which the total angular momentum ͑omitting nuclear spin͒ is a good quantum number. In addition, we demonstrate that the spectral response for tuning the DUMP laser is a simple Lorentzian in free-jet experiments. We test our theoretical results and demonstrate the applicability of RFWM-SEP to jet-cooled, transient species in experiments on C 3 and HCO. Using the well-studied à 1 ⌸ u -X 1 ⌺ g ϩ system of C 3 , we illustrate and compare the two possible schemes for RFWM-SEP. These are defined as 1 ϭ 2 ͑PUMP͒ and 3 ϭ 4 ͑DUMP͒ or 1 ϭ 4 ͑PUMP͒ and 2 ϭ 3 ͑DUMP͒, where 1 , 2 , and 3 are the input frequencies and 4 is the signal frequency. Using the B 2 AЈ -X 2 AЈ system of HCO, we obtain RFWM-SEP spectra that probe ground-state vibrational resonances lying above the low threshold for dissociation to HϩCO. Varying the polarization of the input beams or PUMP rotational branch produce dramatic effects in the relative intensities of rotational lines in the RFWM-SEP spectra of HCO; these effects are well-described by our theoretical analysis. Finally, RFWM-SEP spectra of HCO resonances that are homogeneously broadened by dissociation are consistent with the theoretically predicted Lorentzian line shape; the full widths for these levels are in good agreement with those determined via unsaturated fluorescence depletion SEP.

A pulsed-laser double resonance technique provides previously unavailable spectroscopic data on the rovibrational structure of Ã 1Au acetylene (C2H2). Our assignment and analysis of transitions to the à state ν4′ (torsion) and ν6′ (antisymmetric in-plane bend) vibrational fundamentals uncovers a strong Coriolis interaction between these two nearly degenerate modes and weaker Coriolis interactions between the ν4′/ν6′ pair and remote à state rovibrational levels. We deperturb the direct Coriolis interaction between ν4′ and ν6′ to obtain vibrational frequencies, Coriolis coupling constants and partially deperturbed rotational and centrifugal distortion constants for these previously unobserved fundamentals. Parity selection rules for the Ã←X̃ band permit an unambiguous assignment of the vibrations (ν4′=764.9±0.1 cm−1 and ν6′=768.3±0.2 cm−1). We use these new experimental values to reassign several à state vibrations and to assign previously unidentified à state levels. We also identify two vibrational resonances that seem to be important in determining the rovibrational structure of à 1Au C2H2.

Collisional energy transfer probabilities of highly excited molecules from KCSI. III. Azulene: P(E′,E) and moments of energy transfer for energies up to 40000 cm−1 via self-calibrating experiments

Recent experimental results permit a detailed normal modes analysis of Ã-state acetylene (C2H2) and its isotopomers (C2HD and C2D2). Using only experimentally determined frequencies and measured or estimated anharmonicities, we determine harmonic frequencies for the 11 directly observed and unambiguously assigned vibrational fundamentals. The normal modes calculation varies force constants to fit the 11 harmonic frequencies and yields a complete set of harmonic frequencies, force constants, and Coriolis coefficients for the three isotopomers. A complete set of fundamental frequencies calculated from the set of harmonic frequencies allows a comparison to and, in some cases, suggests a reassessment of frequencies for tentatively assigned fundamental vibrations.