The photodissociation of glyoxal has been investigated by monitoring the CO internal energy distribution using tunable vacuum ultraviolet laser-induced fluorescence on the A←X system. Appearance times for the CO are in excellent agreement with the glyoxal fluorescence decay times, indicating that there is no long-lived intermediate in the dissociation. The quantum yield for CO production is independent of the K quantum number describing the glyoxal rotation. The CO is formed almost entirely in v=0 but is spread over a broadly excited rotational distribution peaking at J≂42. Analysis of the CO Doppler profiles shows that the velocity of the CO increases with increasing rotational level and that the CO recoil velocity vector is oriented predominantly perpendicular to its angular momentum vector. These observations, which are in agreement with both previous time-of-flight data and molecular orbital calculations, are consistent with a model for the dissociation involving planar intermediates for the two channels leading to CO+H2CO or to 2 CO+H2. It appears that the highest rotational levels of CO are produced in coincidence with the H2CO channel.

The lowest electronically excited states of Na2 are of interest as intermediaries in the excitation of higher states and in the development of methods for producing cold molecules. We have compiled previously obtained spectroscopic data on the A 1Sigmau+ and b 3Piu states of Na2 from about 20 sources, both published and unpublished, together with new sub-Doppler linewidth measurements of about 15,000 A<--X transitions using polarization spectroscopy. We also present new ab initio results for the diagonal and off-diagonal spin-orbit functions. The discrete variable representation is used in conjunction with Hund's case a potentials plus spin-orbit effects to model data extending from v=0 to very close to the 3 2S+3 2P12 limit. Empirical estimates of the spin-orbit functions agree well with the ab initio functions for the accessible values of R. The potential function for the A state includes an exchange potential for S+P atoms, with a fitted coefficient somewhat larger than the predicted value. Observed and calculated term values are presented in an auxiliary (EPAPS) file as a database for future studies on Na2.

Articles you may be interested inA guidedion beam study of the hydrogen atom transfer reaction of stateselected N+ 2 with H2 at collision energies ranging from subthermal to 2 eV (c.m.)A twolaser pulseandprobe study of TR, V energy transfer collisions of H+NO at 0.95 and 2.2 eV Collisional energy transfer from H atoms to CO (v = 0, J"", 2) has been studied at a collision energy of 1.S8 ± 0.07 eV by photolyzing H 2 S at 222 nm in a nozzle expansion with CO and probing the CO(v", J") levels using tunable VUV laser-induced fluorescence. The ratio CO (v" = 1) ICO (v" = 0) is found to be 0.1 ± 0.008. The rotational distribution of CO(v" = 0) peaks atJ" ,11 and decays gradually; population is still observed atJ">4S. The rotational distribution of CO (v" = 1) is broad and peaks near J" = 20. The experimental results are compared to quasiclassical trajectory calculations performed both on the H + CO surface of Bowman, Bittman, and Harding (BBH) and on the surface of Murrell and Rodriguez (MR). The experimental rotational distributions, particularly those for CO (v" = 1), show that the BBH surface is a better model than the MR surface. The most significant difference between the two surfaces appears to be that for energetically accessible regions of configuration space the derivative of the potential with respect to the CO distance is appreciable only in the HCO valley for the BBH surface, but is large for all H atom approaches in the MR potential. Because the H-CO geometry is bent in this valley, vibrational excitation on the BBH surface is accompanied by appreciable rotational excitation, as observed experimentally.

Correlations between either scalar or vector quantities measured in the study of photodissociation dynamics can serve to provide a very detailed picture of the dissociative event. This article discusses the use of Doppler profile and time-of-flight spectroscopy to learn about the correlation between the separate internal energies of two recoiling fragments, to study the way in which the internal energy distribution of a fragment varies with its recoil direction and to determine the angle between a photofragment's recoil velocity direction and its rotation vector. Two new techniques are introduced. High-voltage switching of the potential applied to a time-of-flight mass spectrometer is used to map the velocity distribution of photofragments onto their arrival time distribution. Probing of photofragments by polarized light with sub-Doppler resolution is used to determine the degree of angular correlation between their rotation vector and their recoil velocity vector.

The technique of modulated gain spectroscopy has provided detailed information about the shape of the Na2 B 1Πu state potential barrier to dissociation. By measuring the rotation–vibration energies (to ±0.006 cm−1) of all (v′=27–33) quasibound vibrational levels and the rotation-dependent tunneling rates (as obtained from linewidth measurements) of the highest quasibound vibrational level, v′=33, we have been able to characterize this barrier. Our studies show that the barrier height is U(rmax,J=0)=375.2±3.9 cm−1, relative to the center of gravity of the Na(3s)+Na(3p) atomic limit, and the barrier maximum is located at rmax=6.85±0.02 Å.