Photodissociation dynamics of cyanogen (C2N2) in the threshold region for dissociation

Classical phase space theory for product state distributions with application to the v–j vector correlation

“…13,[40][41][42][43] Photodissociation in the ultraviolet yields two CN radicals in their ground X 2 ⌺ states. At shorter separations these doublet states couple together to form an attractive singlet and a repulsive triplet with the dynamics apparently dominated by the motion on the singlet state.…”

“…In many ways this dissociation is a prototypical barrierless reaction and PST accurately models many aspects of the dissociation process. [40][41][42][43] However, the most recent experimental study by Wu and Hall of the vector and scalar correlations in the CN rotational and translational distributions has raised questions regarding the accuracy of PST models of this reaction. 13 In particular, Wu and Hall's comparisons of the experimentally observed Doppler profiles for a specific rovibronic state of one of the CN fragments with the PST predictions indicated that good agreement can only be obtained between PST and experiment when the dissociation energy is assumed to be considerably lower than that estimated from prior studies.…”

Vector and scalar correlations in statistical dissociation: The photodissociation of NCCN at 193 nm

“…Although a small rotational alignment of CN fragments was reported by Lin et al 30 at 206.1 nm, more extensive subsequent work by Wannenmacher et al 31 concluded that the alignment was negligible at multiple excitation energies closer to the dissociation threshold than at 193.3 nm. We have looked for rotational alignment at 193.3 nm, where faster dissociation might be expected to preserve some laboratory-frame anisotropy, by measuring the intensity ratio of the nascent ͑2-0͒ Q 1 13.5 line and its R 12 satellite for two different photolysis polarization directions.…”

“…A previously published PST fit to the vϭ0 rotational distribution was shown by EGM 15 with an available energy of 4600 cm Ϫ1 and b max ϭ2.5 Å, a calculation which we cannot reproduce. Wannenmacher et al 31 also reported problems with these PST calculations, and stated that the jet-cooled data of EGM, as well as their own data at room temperature and longer photolysis wavelengths could be well described by PST calculations if b max is adjusted down to 1.8 Å, using a bond dissociation energy corresponding to 4600-4800 cm Ϫ1 of available energy at 193.3 nm. We find that these parameters also overestimate the population of the high rotational states in the jet-cooled data, although the states with NϽ30 are described reasonably well.…”

“…30,31 The agreement was considered satisfactory, although more recent Doppler measurements in this laboratory 6 indicated that the statistically partitioned energy is less than the full asymptotic energy, and that the vector correlations were too strong to be statistical. 11 Recently we have developed a time-resolved spectrometer based on a frequency modulation ͑FM͒ scheme that permits the measurement of real-time kinetics of chemical processes with submicrosecond time resolution and high sensitivity.…”