Dynamics of H2O2 photodissociation: OH product state and momentum distribution characterized by sub-Doppler and polarization spectroscopy

Abstract

Hydrogen peroxide has been optically excited at a wavelength of 266 nm and the OH photofragment completely characterized by Doppler and polarization spectroscopy using the laser-induced fluorescence technique. The entire internal state distribution (vibration, rotation, spin, and A components), translational energy, angular distribution, rotational alignment, and vector correlations between rotational and translation motions of OH products is measured. The hydroxyl radicals are formed in the X 211 3/2 ,112 ground state with 90% of the available energy (248 kJ/mol) being released as OH recoil translation. The angular distribution is nearly a sin 2 () distribution about the electric vector of the photolysis laser. The internal motion ofOH is vibrationally cold (no vibrationally excited OH was found) while the rotational excitation in v" = 0 can be described by a Boltzmann distribution with a temperature parameter of Trot = (1530 ± 150) K. The two spin states are found to be populated nearly statistically, in contrast to the A components which show an increasing inversion with increasing OH rotation. The observed profiles of recoil Doppler broadened spectral lines are strongly dependent on the nature ofthe transition, the excitation-detection geometry, and the relative polarizations of the dissociating and analyzing laser light. However, the line intensities show only a minor dependence on geometry and polarization indicating a low alignment of OH photofragments (A ~2) ';;;0.1). For the first time the vector correlation between product rotational and translational motions was analyzed and evaluated in terms of the three bipolar moments {3 ~ (20), {3 g (22), and {3 ~ (22). The bipolar moment {3 ~ (20) corresponds to the conventionally defined anisotropy parameter {3 = 2{3 ~ (20) = -0.71. The angular distribution peaks in the direction perpendicular to the electric vector of the dissociating laser light, indicating the predominant electronic excited state in H 2 0 2 being of IA symmetry. The moment {3 g (22) increases with J OH showing a bias towards VOH and J OH being parallel to one another. The moment {3 ~ (22) is a measure of the mutual correlation of the fragment translational and rotational vectors and the transition dipole vector .... in the parent molecule. The positive value of this moment [{3 ~ (22) = 0.11] indicates that the expectation value of (J;) should be very small when .... is parallel to the z axis and VOH perpendicular to .... (x axis). (J!) originates in the torsional motion in the H 2 0 2 parent molecule, while (J;) reflects the bending vibration of nearly planar H 2 0 2 where the H atoms are in the trans position.

Adsorption of hydrogen peroxide on functionalized mesoporous silica surfaces

“…This phenomenon can be explained by formation of hydrogen bonds between free silanol groups and hydrogen peroxide. In the experimental conditions, almost all of silanol groups were ionized as mesoporous silanol groups existed in two forms, Si-(OH) 2 and Si-(OH) with pK a values, respectively, 8.2 and 2.0 [49]. …”

“…Hydrogen peroxide is a very useful oxidizer that has been employed in many different fields, such as chemistry of atmosphere [1], autodissociation dynamics [2,3], and bleaching [4]. It is reasonably stable, readily available, inexpensive, and generates only water as a by-product [5].…”

Photodissociation Dynamics

“…For example, H 2 CO is known to dissociate mainly to CO(V)0), so from Doppler profiles of the H 2 fragment one could determine the correlation between H 2 (V,J) levels and average CO (V)0) rotational excitation, demonstrating that the latter decreases with increasing vibrational excitation of the H 2 . 32 While the energy resolution provided by Doppler spectroscopy is somewhat limited, the real power of Doppler/LIF measurements was demonstrated in a series of experimental [72][73][74][75] and theoretical 76 papers published in 1986. These studies showed that the shapes of Doppler profiles are sensitive to the photofragment alignment.…”

Theoretical Study on the Urea−Hydrogen Peroxide 1:1 Complexes

“…Given the considerable usefulness of hydrogen peroxide in many fields, such as atmospheric chemistry, 1 photodissociation dynamics, [2][3][4][5][6] and oxidation reactions, 7 and of urea in biological processes because of potential hydrogen-bonding and acidbase properties associated with both the amine and the carbonyl groups, the ureashydrogen peroxide (UHP) 1:1 complex has been widely used in several oxidation processes [8][9][10][11][12] and also as a safe source to produce hydrogen peroxide. 13 The crystal structure of UHP 1:1 complex was first experimentally investigated by X-ray 14 and later by neutron diffraction at low temperatures.…”