Femtosecond Photolysis of ClO₂ in Aqueous Solution

Abstract

The photolysis of aqueous ClO2 has been studied with a new femtosecond transient absorption spectrometer, allowing absorbance changes as small as ΔA ≈ 1 × 10-4 to be recorded with a time resolution of 150 fs. ClO2 was photolyzed at 390 nm and the ultrafast formation and decay of photoproducts were monitored at 260, 390, and 780 nm. As expected from earlier studies, Cl atoms are formed with a quantum yield of Φ(Cl) = 0.1. However, the rate of formation is nearly 2 orders of magnitude higher than that reported. Moreover, Cl is the only photoproduct that survives 25 ps after the photolysis pulse. The main photolytic products, ClO + O, formed with a quantum yield of 0.9, disappear through fast geminate recombination, producing vibrational excited ClO2 in the electronic ground state. The vibrational relaxation of this species occurs with a time constant of 10 ps. The vanishing yield of cage escape for ClO + O, which contrasts with the reported result of the photolysis at 355 nm, indicates that the amount of excess energy imparted to these products at 390 nm is insufficient to enable them to separate. The decay of a photoinduced dichroism observed at 390 nm is interpreted as an orientational relaxation of ground-state ClO2 , the time constant (0.6 ps) agreeing with that calculated from the hydrodynamical slip model.

Photodissociation and Vibrational Relaxation of OClO at Liquid Surfaces

“…The photodissociation of OClO to give (a) OCl + O, or (b) Cl + O 2 , has been extensively studied in the gas phase [1][2][3][4][5] and in bulk liquids [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] due to its possible environmental impact. 22 These studies have contributed to the basic understanding of the nature of the excited-state potentials and the specific solvent-solute interactions that give rise to the observed quantum yield of the different photoproducts and the vibrational relaxation rate of the recombined OClO.…”

Determination of differential quantum yields in solution by electron paramagnetic resonance spectroscopy

“…Although studies on the photolysis of OC10 have increased since it was determined as one of the main processes related to the destruction of the stratospheric ozone, most of the works on this topic refer to the primary processes [5][6][7][8][9][10][11][12][13][14][15]:…”

“…In water, the reported distribution among the two channels is indicated in parentheses [11]. Two allowed mechanisms are possible for reaction (1): direct dissociation or isomerization to CIOO and subsequent dissociation into CI + 02.…”

Kinetics and Mechanism of Catalytic Decomposition and Oxidation of Chlorine Dioxide by the Hypochlorite Ion

“…While this reaction is one of the possible fragmentation * To whom correspondence should be addressed. (1) channels in condensed-phase photolysis of chlorine dioxide, [22][23][24][25][26][27][28][29] it does not seem to be feasible in the thermally induced decomposition. In support of this statement, it should be remembered that slightly acidic solutions of chlorine dioxide can be stored in the dark without apparent concentration loss for several months.…”