HCl elimination in the photolysis of chlorobenzene at 266 nm: An FT-IR spectroscopy and quantum chemical study

Charge-Separated Reactive Intermediates from the UV Photodissociation of Chlorobenzene in Solution

“…In an Ar matrix, ortho -benzyne has an electronic absorption band at ∼377 nm, and previous transient absorption experiments reported a 370 nm band assigned to an intermediate containing an ortho -benzyne moiety . A similar structure to those considered here for the iso -PhCl complexes was recently computed by Behera et al, who suggested its involvement in HCl elimination from the 266 nm photolysis of gas-phase PhCl . They observed ro-vibrational spectral lines assigned not only to HCl but also to acetylene (C 2 H 2 ) and 1,3-butadiyne (C 4 H 2 ) which may arise from further degradation of internally excited ortho -benzyne …”

“… 82 A similar structure to those considered here for the iso -PhCl complexes was recently computed by Behera et al, who suggested its involvement in HCl elimination from the 266 nm photolysis of gas-phase PhCl. 83 They observed ro-vibrational spectral lines assigned not only to HCl but also to acetylene (C 2 H 2 ) and 1,3-butadiyne (C 4 H 2 ) which may arise from further degradation of internally excited ortho -benzyne. 83 …”

“… 83 They observed ro-vibrational spectral lines assigned not only to HCl but also to acetylene (C 2 H 2 ) and 1,3-butadiyne (C 4 H 2 ) which may arise from further degradation of internally excited ortho -benzyne. 83 …”

“…The lifetime of the S 1 state approaches 1 ns, yet most of the population in the S 1 state does not return to the ground state because the ground-state bleach features observed by TVAS do not recover significantly on this time scale. The reaction pathways of photoexcited PhCl (S 1 , 1 ππ*) were previously suggested to be homolytic bond cleavage to Ph + Cl radicals, 29 , 30 HCl elimination, 83 and ISC to the T 1 state. 84 Here, we propose a solvent-sensitive reaction pathway that involves the formation of intermediates argued to be isomers of PhCl (denoted as iso -PhCl) with pronounced charge-transfer character.…”

“…82 A similar structure to those considered here for the iso-PhCl complexes was recently computed by Behera et al, who suggested its involvement in HCl elimination from the 266 nm photolysis of gas-phase PhCl. 83 They observed ro-vibrational spectral lines assigned not only to HCl but also to acetylene (C 2 H 2 ) and 1,3butadiyne (C 4 H 2 ) which may arise from further degradation of internally excited ortho-benzyne. 83 Transient vibrational absorption spectra obtained for the same two solutions of PhCl, but using a UV excitation wavelength of 270 nm and a mid-IR probe pulse spanning 1470−1630 cm −1 , are shown in Figure S8 of the Supporting Information.…”