Molecular beam cooled HCl was state selected by two-photon excitation of the , , and states through either the or lines of the respective transition. Similarly, HBr was excited to the [, ], , and states through the or lines. Following absorption of a third photon, protons were formed by three different mechanisms and detected using velocity map imaging. (1) was formed in coincidence with halogen atoms and subsequently ionized. For HCl, photodissociation into was dominant over the formation of and was attributed to parallel excitation of the repulsive superexcited states. For HBr, the ratio decreases with increasing excitation energy. This indicates that both the and the superexcited states contribute to the formation of . (2) For selected intermediate states HCl was found to dissociate into the ion pair with over 20% relative yield. A mechanism is proposed by which a bound superexcited state acts as a gateway state to dissociation into the ion pair. (3) For all intermediate states, protons were formed by dissociation of following a parallel, , excitation. The quantum yield for the dissociation process was obtained using previously reported photoionization efficiency data and was found to peak at for HCl and for HBr. This is consistent with excitation of the repulsive and states of , and the state of . Rotational alignment of the intermediate states is evident from the angular distribution of the excited photofragments. This effect has been observed previously and was used here to verify the reliability of the measured spatial anisotropy parameters.
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28 September 2007
Research Article|
September 25 2007
Proton formation in resonance enhanced multiphoton excitation of HCl and HBr via Rydberg and ion-pair states
Constantin Romanescu;
Constantin Romanescu
Department of Chemistry,
Queen’s University
, Kingston, Ontario K7L 3N6, Canada
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Hans-Peter Loock
Hans-Peter Loock
a)
Department of Chemistry,
Queen’s University
, Kingston, Ontario K7L 3N6, Canada
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a)
Author to whom correspondence should be addressed, Tel.: 1-613-533-2621. Electronic mail: [email protected]
J. Chem. Phys. 127, 124304 (2007)
Article history
Received:
May 07 2007
Accepted:
July 05 2007
Citation
Constantin Romanescu, Hans-Peter Loock; Proton formation in resonance enhanced multiphoton excitation of HCl and HBr via Rydberg and ion-pair states. J. Chem. Phys. 28 September 2007; 127 (12): 124304. https://doi.org/10.1063/1.2767259
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