Intermolecular hydrogen bonding in chlorine dioxide photochemistry: A time-resolved resonance Raman study

Femtosecond pump-probe studies of actinic-wavelength dependence in aqueous chlorine dioxide photochemistry

The actinic or photolysis-wavelength dependence of aqueous chlorine dioxide (OClO) photochemistry is investigated using femtosecond pump-probe spectroscopy. Following photoexcitation at 310, 335, and 410 nm the photoinduced evolution in optical density is measured from the UV to the near IR. Analysis of the optical-density evolution illustrates that the quantum yield for atomic chlorine production (Phi(Cl)) increases with actinic energy, with Phi(Cl)=0.16+/-0.02 for 410 nm excitation and increasing to 0.25+/-0.01 and 0.54+/-0.10 for 335 and 310 nm excitations, respectively. Consistent with previous studies, the production of Cl occurs through two channels, with one channel corresponding to prompt (<5 ps) Cl formation and the other corresponding to the thermal decomposition of ClOO formed by OClO photoisomerization. The partitioning between Cl production channels is dependent on actinic energy, with prompt Cl production enhanced with an increase in actinic energy. Limited evidence is found for enhanced ClO production with an increase in actinic energy. Stimulated emission and excited-state absorption features associated with OClO populating the optically prepared (2)A(2) surface decrease with an increase in actinic energy suggesting that the excited-state decay dynamics are also actinic energy dependent. The studies presented here provide detailed information on the actinic-wavelength dependence of OClO photochemistry in aqueous solution.

FTIR studies of intermolecular hydrogen bonding in halogenated ethanols

The effect of halogen substitution on intermolecular hydrogen-bonding in ethanol is studied. Specifically, Fourier-transform infrared (FTIR) spectra of ethanol, 2,2,2-trifluoroethanol (TFE), and 2,2,2-trichloroethanol dissolved in carbon tetrachloride are reported as a function of temperature and concentration. The spectral intensities corresponding to monomer, dimer, and multimer formation are used to determine the effect of halogen substitution on intermolecular hydrogen-bonding. The enthalpy for dimerization was found to evolve from -4.2+/-0.3 kcal/mol in ethanol to -6.8+/-1.0 kcal/mol in TFE. An opposite trend was observed for multimer formation with enthalpies of -3.7+/-0.5 in ethanol and -2.1+/-1.4 kcal/mol in TFE. The majority of this evolution is assigned to the ability of ethanols to form intramolecular hydrogen bonds involving the hydoxyl proton and the halogen substituents.