Characterization of iso-CF2I2 in frequency and ultrafast time domains

Abstract

The photolysis of diiododifluoromethane (CF(2)I(2)) in condensed phases was studied by a combination of matrix isolation and ultrafast time-resolved spectroscopy, in concert with ab initio calculations. Photolysis at wavelengths of 355 or 266 nm of CF(2)I(2):Ar samples (1:5000) held at approximately 8 K yielded iso-CF(2)I(2) (F(2)C-I-I), a metastable isomer of CF(2)I(2), characterized here for the first time. The infrared (IR) spectra of this isomer were recorded in matrix experiments, and the derived positions of the C-F stretching modes are in very good agreement with the predictions of high level ab initio calculations, which show that the iso-form is a minimum on the CF(2)I(2) ground state potential energy surface. The formation of this isomer following 350 nm excitation of CF(2)I(2) in room temperature CCl(4) solutions was monitored through its intense C-F stretching mode by means of ultrafast time-resolved IR absorption. Together, matrix isolation and ultrafast IR absorption experiments suggest that the formation of iso-CF(2)I(2) occurs via recombination of CF(2)I radical and I atom. Ultrafast IR experiments detect a delayed rise of iso-CF(2)I-I absorption, placing an upper limit of 400 fs for the C-I bond dissociation and primary geminate recombination processes. The product absorption spectrum recorded 1 ns after 350 nm excitation of CF(2)I(2) in solution is virtually identical to the visible absorption spectrum of iso-CF(2)I(2) trapped in matrix isolation experiments [with subtracted I(2)(X) absorption]. The formation of this isomer in solution at room temperature has direct dynamic implications for the ultrafast production of molecular iodine from electronically excited CF(2)I(2).

Roaming-mediated ultrafast isomerization of geminal tri-bromides in the gas and liquid phases

“…This isomerization pathway could be termed 'roamingmediated', because it involves the migration of the incipient bromine fragment and leads to the iso product species; however, this could not be confirmed without comparison to the same reaction in the gas phase. The isomeric form occupies a shallow minimum on the potential energy surface (PES)-somewhat below the C-Br bond radical dissociation asymptote [12][13][14][15] -and has been proposed 16 to be accessible on the way towards molecular bromine from photoexcited bromoform in the gas phase. This isomerization pathway in the gas phase can only occur through the internal rearrangement of atoms, that is, directly and without the involvement of any other species.…”

When isomerisation is electron transfer: the intriguing story of the iso-halocarbons

“…The ubiquitous nature of the isomers is underscored by the fact that they are products of both radiolysis [43][44][45][46][47] and photolysis [50][51][52][53][54][55] of isolated halocarbons; moreover, spectra of several iso-halocarbons have been recently rediscovered in experiments where the parent was co-deposited with ablated metal atoms [56]. Experimental probes of the iso-halocarbons: complementarity of time-resolved and steady state measurements The initial characterisation of the iso-halocarbons came, as described above, in studies in frozen glasses and inert matrices.…”

Solvent dependent branching between C-I and C-Br bond cleavage following 266 nm excitation of CH2BrI

“…4,[25][26][27] Cage-enhanced geminate recombination has significant yield to the iso products and these products have been observed in variety of different experiments. 3,25,26,[28][29][30][31][32][33][34][35][36][37][38][39][40][41][42] Ultraviolet excitation of CH 2 BrI yields iso-CH 2 Br-I or iso-CH 2 I-Br following C-I or C-Br bond cleavage, respectively. These products are predicted to have transitions in the visible or near UV with very large oscillator strength (∼0.5).…”