Spin polarization in SO photochemically generated from SO2

Abstract

The photochemical processes induced in sulfur dioxide by 193 nm excimer laser excitation have been investigated by examining vibration-rotation transitions of the reaction product SO with the use of tunable infrared diode-laser spectroscopy. Only X 3Σ− ground-state SO molecules were observed. About 70% of the nascent SO molecules were found to be in the v=2 state, about 20% in v=1, and some in v=5. The rotational distribution in each vibrational state differed significantly from the thermal distribution, and was shifted towards higher rotational levels in lower vibrational states. The electron spin was observed to be polarized in the v=1 and 2 states in a direction either parallel or antiparallel to the rotational angular momentum, i.e., the F1 and F3 spin sublevels are more populated than the F2 level in these states. This selective population was not observed for v=5. The origin of the spin polarization is discussed in terms of spin-orbit mixing between the C̃ state and a repulsive triplet state of SO2. The results obtained here emphasize the usefulness of high resolution, high sensitivity infrared laser spectroscopy in the study of primary processes in photochemistry.

A chirped-pulse Fourier-transform microwave/pulsed uniform flow spectrometer. II. Performance and applications for reaction dynamics

“…It should be mentioned, however, that measurement of higher rotational states could also provide valuable insight, as it has been noted that there is a shift in population toward higher rotational levels in lower vibrational levels. 28,31,32 The very rapid vibrational relaxation observed here is likely owing to the near resonance of the SO fundamental (1149 cm −1 ) with the SO 2 symmetric stretch (1151 cm −1 ), possibly giving rise to very efficient v-v energy transfer. 18 The fact that v = 2 continues to dominate over v = 1 even as v = 0 becomes dominant is a puzzling feature that may be the result of additional underlying resonant relaxation pathways.…”

“…24,25,27,30 These conclusions were drawn, in part, from the observation of inverted vibrational distributions in the SO fragment, where >50% of the population is in the v = 2 vibrational level rather than the ground v = 0 state (Table I). 24,26,27,31 The CPUF spectrometer was used to probe the nascent vibrational distribution of SO following photodissociation of SO 2 . The SO 2 (Sigma Aldrich, 99.9%) was seeded at 0.5% in the helium flow and dissociated using an ArF excimer laser.…”

“…Our approach to generating pulsed uniform supersonic flows is based on an axisymmetric Laval nozzle and a novel high-throughput piezoelectric stack valve that has been described and characterized in Paper I. 20 The flow system has been developed and integrated into a new CP-FTMW spectrometer operating in the K a -band (26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40). 20 We term this combination a Chirped-PulseUniform Flow (CPUF) spectrometer.…”

Spectroscopy and structures of free radicals and molecular ions

“…Recently, some high-resolution time-resolved spectroscopic observations have become feasible for these transient species [109,110]. This trend will continue and will open a new epoch for studies of chemical reactions.…”

Millimeter-wave optical double resonance schemes for rapid assignment of perturbed spectra, with applications to the C̃1B2 state of SO2

“…1 Thus, theC state plays an important role in the photodissociation of SO 2 in the earth's atmosphere. However, there is evidence for more than one dissociation mechanism, including vibronic coupling to the dissociation continuum of the groundX electronic state, 2-4 intersystem crossing to one or more dissociative triplet states, 1,[5][6][7] and a singlet mechanism due to avoided crossing with the dissociative 3 1 A ′ state. 8,9 It is likely that all three mechanisms contribute, and that the relative contribution depends on the energy.…”