Photodissociation Dynamics of Phenol

Abstract

The photodissociation of phenol at 193 and 248 nm was studied using multimass ion-imaging techniques and step-scan time-resolved Fourier-transform spectroscopy. The major dissociation channels at 193 nm include cleavage of the OH bond, elimination of CO, and elimination of H(2)O. Only the former two channels are observed at 248 nm. The translational energy distribution shows that H-atom elimination occurs in both the electronically excited and ground states, but elimination of CO or H(2)O occurs in the electronic ground state. Rotationally resolved emission spectra of CO (1 <or= v <or= 4) in the spectral region of 1860-2330 cm(-1) were detected upon photolysis at 193 nm. After a correction for rotational quenching, CO (v <or= 4) shows a nascent rotational temperature of approximately 4600 K. The observed vibrational distribution of (v = 1)/(v = 2)/(v = 3)/(v = 4) = 64.3/22.2/9.1/4.4 corresponds to a vibrational temperature of 3350 +/- 20 K. An average rotational energy of 6.9 +/- 0.7 kcal mol(-1) and vibrational energy of 3.8 +/- 0.7 kcal mol(-1) are observed for the CO product. The dissociation channels, translational energy distributions of the photofragment, and vibrational and rotational energies of product CO are consistent with potential energy surfaces from quantum chemical calculations and the branching ratios from an RRKM calculation.

A Multipronged Comparative Study of the Ultraviolet Photochemistry of 2-, 3-, and 4-Chlorophenol in the Gas Phase

“…8 Analogy with previous studies of chlorobenzene photolysis 35 led Yamamoto et al 13 to suggest intersystem crossing to a 3 * state (the equilibrium geometry for which involved an 22 In what follows, we thus look again for singlet state only (i.e. spin conserving) routes to explain the observed photochemistry of the gas phase chlorophenols.…”

“…These have not been estimated in the present work, but we can anticipate their relative rates (and their variation with excitation energy) by reference to the earlier study of phenol photolysis. 8 As in that study, fig. 8 2-ClPhOH, syn 35892 [13] ~8.9 [29] 2-ClPhOH, anti 35702 [13] 3-ClPhOH, syn 35769 [15] 8.65 [15] 3-ClPhOH, anti 35889 [15] 8.68 [15] 4-ClPhOH 34811 [11] 8.44 [10] Figure Captions …”

“…8 Such complexity can be expected to increase upon extending to substituted phenols, as illustrated in the present work for the case of chlorophenols (henceforth ClPhOH). These systems offer the possibility of additional dissociation pathways (e.g.…”

“…8 shows, the lowestenergy barriers leading to these products in some cases lie below the asymptotes for direct bond cleavage. The variational TSs leading to bond cleavage will be significantly looser than the saddle-point TSs involved in molecular elimination, but the earlier RRKM studies 8 suggest that the molecular elimination pathways will dominate, at least at lower energies. Suitable isomerisation TSs have also been located at sufficiently low energies to permit rapid interconversion between the isomers prior to dissociation.…”

The near ultraviolet photodissociation dynamics of 2- and 3-substituted thiophenols: Geometric vs. electronic structure effects

“…Such fragmentation dynamics have been demonstrated in phenol [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] and thiophenol, [24][25][26][27][28][29][30] in a range of substituted phenols [31][32][33][34][35][36] and thiophenols, [37][38][39] and in the methylated analogues anisole 40,41 and thioanisole, [42][43][44][45][46] in both the gas and condensed [47][48][49][50] phase. The present study focusses on thiophenols and, particularly, how the much-studied S-H bond fission process is affected by asymmetric substitution (i.e., in the 2-and 3-positions) of the aromatic ring.…”