No abstract

We have measured the polarized infrared absorption spectrum of the allyl radical, CH2CHCH2 (X̃) 2A2, in an argon matrix at 10 K. The experimental CH2CHCH2 frequencies (cm-1) and polarizations follow:  a1 modes, 3109, 3052, 3027, 1478, and 1242; b1 modes, 983, 801, and 510; b2 modes, 3107, 3020, 1464, 1390, and 1182. Two modes (ν6 and ν18) are very weak and could not be detected; the lowest frequency a1 mode (the CH2−CH−CH2 bending mode ν7) is estimated to be beyond the wavelength range of our MCT infrared detector. Infrared absorption spectra of two deuterated isotopomers, CH2CDCH2 and CD2CDCD2, were recorded in order to compare experimental frequency shifts with calculated [UB3LYP/6-311-G(d,p)] harmonic frequencies. Linear dichroism spectra were measured with photooriented samples in order to establish experimental polarizations of most vibrational bands. True gas-phase vibrational frequencies were estimated by considering the gas-to-matrix shifts and matrix inhomogeneous line broadening. The allyl radical matrix frequencies listed above are within ±1% of the gas-phase vibrational frequencies. A final experimental set of all the vibrational frequencies for the allyl radical are recommended. See also: .

No abstract

Gas-phase photodissociations of cyclopropyl iodide were conducted at 266 and 279.7 nm, and the radical products were probed by multiphoton ionization, with imaging of the resulting ions and their corresponding electrons. Solution-phase photodissociations of cyclopropyl iodide were also conducted with TEMPO-trapping of the radical dissociation products. In both gas and solution phases, allyl radical was found to be a direct product of the cyclopropyl iodide photodissociation. CASSCF calculations indicate that the allyl radical could be formed directly from photoexcited cyclopropyl iodide by way of two surface crossings between open- and closed-shell potential energy surfaces. Each surface crossing represents a point of potential bifurcation in the reaction dynamics. Thus, cyclopropyl iodide that is excited to a 1(n,σ*) state can remain on an open-shell surface and generate the cyclopropyl radical and an iodine atom or can cross to a closed-shell (ion-pair) surface. The cyclopropyl cation that results from the surface crossing can undergo barrierless ring opening to the allyl cation before crossing back to an open-shell surface to generate allyl radical and an iodine atom. In this manner, both cyclopropyl radical and allyl radical can be formed as direct products of cyclopropyl iodide photodissociation.

The mechanistic aspects of the photochemistry of several iminosulfonate photoacid generators (PAGs) have been studied based on product analysis, nanosecond laser flash photolysis, and determination of acid generation efficiencies. Our findings support a competition between homolytic and heterolytic N-O dissociation mechanisms. By measuring the efficiencies of acid generation for each PAG in the presence and absence of an ion quencher, we were able to roughly quantify the degree of branching between heterolytic and homolytic photocleavage pathways for each PAG. The p-toluenesulfonyloxyl radical was detected upon laser flash photolysis of several PAGs and was found to have a lambda(max) at 540 nm. By quenching the 540 nm transient with a variety of reactive species, the rate constants for reaction of the p-toluenesulfonyloxyl radical with these substrates were determined. The p-toluenesulfonyloxyl radical is shown to be a highly reactive species, which undergoes rapid hydrogen transfer and is a powerful oxidizer.