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

Article abstract of DOI:10.1063/1.451767

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 X²Π_3/2,1/2 ground state with 90percent of the available energy (248 kJ/mol) being released as OH recoil translation.The angular distribution is nearly a sin²θ distribution about the electric vector of the photolysis laser.The internal motion of OH 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 T_rot = (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 of the 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 (A₀⁽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 β₀²(20), β₀⁰(22), and β₀²(22).The bipolar moment β₀²(20) corresponds to the conventionally defined anisotropy parameter β = 2β₀²(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 H2O2 being of ¹A symmetry.The moment β₀⁰(22) increases with J_OH showing a bias towards v_OH and J_OH being parallel to one another.The moment β₀⁰(22) is a measure of the mutual correlation of the fragment translational and rotational vectors and the transition dipole vector W in the parent molecule.The positive value of this moment <β₀²(22) = 0.11> indicates that the expectation value of y²> should be very small when μ is parallel to the z axis and v_OH perpendicular to μ (x axis). X²> originates in the torsional motion in the H2O2 parent molecule, while z²> reflects the bending vibration of nearly planar H2O2 where the H atoms are in the trans position.

Full text of DOI:10.1063/1.451767

Dynamics of H2O2 photodissociation: OH product state and momentum
distribution characterized by subDoppler and polarization spectroscopy
KarlHeinz Gericke, Stefan Klee, Franz Josef Comes, and Richard N. Dixon
Citation: The Journal of Chemical Physics 85, 4463 (1986); doi: 10.1063/1.451767
View online: http://dx.doi.org/10.1063/1.451767
View Table of Contents: http://scitation.aip.org/content/aip/journal/jcp/85/8?ver=pdfcov
Published by the AIP Publishing
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