IR absorption spectra of hexafluorobenzene anions and pentafluorophenyl radicals in solid argon

Photochemical mechanistic study of hexafluorobenzene involving the low-lying states

The photochemical isomerization and nonradiative decay processes of hexafluorobenzene (HFB) were investigated theoretically to gain insights into its photochemical mechanism and the perfluoro effect. A complete mechanistic scheme is presented through the characterization of all the possible minima and transition states of the S0, S1, and S2 states at the CASPT2/6-311G**//CAS(6,7)/6-31G* level. On the S0 potential energy surface, HFB could isomerize to three different products [Dewar-HFB (S0-P1), benzvalene-HFB (S0-P2), and fulvene-HFB (S0-P3)]. Following excitation to the S2 state with the perpendicular π → σ* transition, a chair-type minimum with Cs symmetry was found on the S2 potential energy surface. The adjacent S2/S1 conical intersection was immediately accessible from the S2 minimum. The nature of the S1 state was confirmed to have a π → π* character. Both the S2 and S1 photochemistries of HFB yielded Dewar-HFB via the S1/S0 conical intersection. The regeneration of the S0 state from the S1 and T2 states via intersystem crossing or internal conversion was also revealed.

Photoinduced Dual C-F Bond Activation of Hexafluorobenzene Mediated by Boron Atom

The reaction of laser-ablated boron atoms with hexafluorobenzene (C6 F6 ) was investigated in neon and argon matrices, and the products are identified by matrix isolation infrared spectroscopy and quantum-chemical calculations. The reaction is triggered by a boron atom insertion into one C-F bond of hexafluorobenzene on annealing, forming a fluoropentafluorophenyl boryl radical (A). UV-Vis light irradiation of fluoropentafluorophenyl boryl radical causes generation of a 2-difluoroboryl-tetrafluorophenyl radical (B) via a second C-F bond activation. A perfluoroborepinyl radical (C) is also observed upon deposition and under UV-Vis light irradiation. This finding reveals the new example of a dual C-F bond activation of hexafluorobenzene mediated by a nonmetal and provides a possible route for synthesis of new perfluorinated organo-boron compounds.

Far-UV absorption spectra of SiH2 and dibridged Si2H2 isolated in solid argon

We employ electron bombardment during the deposition of an Ar matrix containing a small proportion of SiH4 to generate various silicon hydrides. Subsequently, the irradiation of a matrix sample at 365 nm decomposes SiH2 and dibridged Si2H2 in solid Ar, which we identify through infrared spectroscopy. We further recorded the corresponding ultraviolet absorption spectra at each experimental stage. An intense band observed in the range of 170-203 nm is largely destroyed upon 365-nm photolysis, which is assigned to the C1B2 ← X1A1 transition of SiH2. Moreover, a moderate band observed in the region of 217-236 nm is reduced slightly, which is assigned to the 31B2 ← X1A1 transition of dibridged Si2H2. These assignments are made based on the observed photolytic behavior, and the prediction of the vertical excitation energies with the corresponding oscillator strengths by using time-dependent density functional theory and equation-of-motion coupled cluster theory.

IR absorption spectra of aniline cation, anilino radical, and phenylnitrene isolated in solid argon

Electron bombardment of aniline (PhNH₂) in an Ar matrix mainly generated the aniline cation (PhNH₂⁺), anilino (PhNH) and phenyl (Ph) radicals, and phenylnitrene (PhN). Further irradiation of the electron-bombarded matrix sample at 365 nm depleted PhNH₂⁺ and PhN, and resulted in the formation of PhNH₂, PhNH, and Ph. In separate experiments, irradiation of the PhNH₂/Ar matrix samples at 265 or 160 nm mainly generated PhNH and Ph radicals, but without the formation of PhNH₂⁺ and PhN. According to the observed photochemical behaviors, quantum-chemically predicted harmonic vibrational wavenumbers of each species, and the information reported in previous photodissociation studies, we unambiguously characterized the IR features of the aromatic species. The information of the vibrational fundamentals of PhNH is new and the formation mechanism is discussed.