On the à and B̃ electronic states of NCO and its clusters with nonpolar solvents

Abstract

The B←X and Ã←X transitions of the NCO radical and its clusters with nonpolar solvents are studied in a supersonic jet expansion by employing laser-induced fluorescence techniques. Fluorescence excitation ͑FE͒ and hole burning spectra are recorded for the NCO radical and compared to previous work. NCO is clustered with Ar, N 2 , CH 4 , and CF 4 nonpolar molecules to elucidate the effect of solvation on the radical energy levels and dynamics. FE spectra are detected for NCO 1:1 clusters showing blue shifts in their spectra with respect to that of the isolated NCO radical, while their 1:n counterparts show either red or blue shifts. Potential energy surface calculations are performed to evaluate the binding energies and geometries of 1:1 clusters in the X, Ã, and B electronic states. The relatively long decay lifetime and red shifted fluorescence wavelength range observed for B state clusters suggests that they decay first through internal conversion ͑IC͒ to à vibronic levels, and then experience rapid intracluster vibrational redistribution ͑IVR͒ and vibrational predissociation ͑VP͒, yielding ground state solvent molecules and NCO radicals at lower à vibronic levels. These à state NCO radicals subsequently emit, generating the Ã→X band.

State-resolved translation energy distributions for NCO photodissociation

“…13,14 Subsequently, there have been several investigations using absorption, 15,16 stimulated emission pumping, [17][18][19] and laser-induced fluorescence ͑LIF͒. [20][21][22][23][24][25][26][27] Additionally, the spectroscopy of the B 2 ⌸ state was examined in the photodissociation experiments by Cyr et al 6 Several of these studies have also provided insight into the dynamical processes that NCO undergoes upon dissociation. Figure 1 illustrates the energy level diagram for NCO and its lowest energy fragmentation channels.…”

Solvation of cyclopentadienyl and substituted cyclopentadienyl radicals in small clusters. I. Nonpolar solvents

“…[14][15][16] In the fluorescence excitation experiments, a general valve pulsed nozzle is used to generate an adiabatic expansion of the appropriate mixture of molecular precursor for Xcpd ͑Ͻ1% of the total pressure͒, the solvent gas ͑0.1%-10% of the total pressure͒, and 50-400 psi He expansion gas. The stainless steel vacuum chamber into which the mixture is expanded remains at ϳ10 Ϫ4 Torr during the FE experiment.…”

“…Nonetheless, relatively few studies involving radicals and clusters can be found in the literature, due in part to the significantly increased difficulties encountered in generating, isolating, cooling, and clustering these short lived, reactive species. Of particular note for cluster studies of radicals are those involving OH-Ne, N 2 , H 2 , 9 NH, CH-rare gases, 10 CN-Ne, 11 C 2 H 3 O-Ar, 12 C 5 H 5 -He, Ne, N 2 , 13 C 5 H 4 CH 3 -He, Ne, 13 and CH 3 O, 14 NCO, 15 and C 6 H 5 CH 2 /Ar, N 2 , CH 4 , C 2 H 6 , and C 3 H 8 . 16 Reports involving vdW clusters of aromatic radicals are limited to the benzyl, cyclopentadienyl, and methylcyclopentadienyl radicals to the best of our knowledge.…”

Solvation of cyclopentadienyl and substituted cyclopentadienyl radicals in small clusters. II. Cyanocyclopentadienyl with polar solvents

“…To model the excited state behavior of Xcpd-nonpolar solvent clusters we employ the Xcpd-Ar cluster data to fit C, H, X parameters under a number of simplifying assumptions. 8,9,12 These parameters are in turn employed to understand the other cluster spectra; in general, this program is reasonably successful.…”