Molecular beams studies of the dissociation of highly excited NO2 induced by molecular colliders

C. R. Bieler, Andrei M Sanov, C. Capellos, H. Reisler

Research output: Contribution to journalArticle

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Abstract

NO2 in high vibrational levels was prepared in a pulsed molecular beam by laser excitation of the mixed 12A1/22B2 state to energies hv below dissociation threshold D0, D0 - hv = 0-500 cm-1. The beam of excited molecules was crossed with pulsed, neat molecular beams of HCl, CO2, N2O, and NH3 at relative collision energies of ∼2000 cm-1, and the NO produced by collision-induced dissociation (CID) was detected state-selectively. The CID yield spectra obtained by monitoring specific NO rotational levels while scanning the excitation wavelength show spectral features identical with those in the fluorescence excitation spectrum of NO2. The yield of the CID products, however, decreases exponentially (compared with the fluorescence spectrum) with the increase of the amount of energy required to reach the threshold of appearance of the monitored NO state. The average energy transferred per activating collision with polyatomic colliders is in the range 130-200 cm-1, having values similar to or lower than those for diatomic and atomic colliders. This is in contrast to deactivating collisions, in which polyatomic colliders are in general more effective. The results are discussed in terms of a mechanism in which the NO2 molecules are activated by impulsive collisions creating a distribution of molecules in quantum states above D0 whose populations diminish exponentially with energy. The collisional activation is followed by unimolecular decomposition. The differences between the activation and deactivation pathways are rationalized in terms of the number of degrees of freedom available for energy transfer in each channel.

Original languageEnglish (US)
Pages (from-to)3882-3887
Number of pages6
JournalJournal of Physical Chemistry
Volume100
Issue number10
StatePublished - Mar 7 1996
Externally publishedYes

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Molecular beams
Colliding beam accelerators
molecular beams
dissociation
collisions
Molecules
Fluorescence
Chemical activation
Laser excitation
Energy transfer
energy
activation
excitation
molecules
fluorescence
thresholds
Decomposition
Scanning
Wavelength
Monitoring

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Molecular beams studies of the dissociation of highly excited NO2 induced by molecular colliders. / Bieler, C. R.; Sanov, Andrei M; Capellos, C.; Reisler, H.

In: Journal of Physical Chemistry, Vol. 100, No. 10, 07.03.1996, p. 3882-3887.

Research output: Contribution to journalArticle

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AB - NO2 in high vibrational levels was prepared in a pulsed molecular beam by laser excitation of the mixed 12A1/22B2 state to energies hv below dissociation threshold D0, D0 - hv = 0-500 cm-1. The beam of excited molecules was crossed with pulsed, neat molecular beams of HCl, CO2, N2O, and NH3 at relative collision energies of ∼2000 cm-1, and the NO produced by collision-induced dissociation (CID) was detected state-selectively. The CID yield spectra obtained by monitoring specific NO rotational levels while scanning the excitation wavelength show spectral features identical with those in the fluorescence excitation spectrum of NO2. The yield of the CID products, however, decreases exponentially (compared with the fluorescence spectrum) with the increase of the amount of energy required to reach the threshold of appearance of the monitored NO state. The average energy transferred per activating collision with polyatomic colliders is in the range 130-200 cm-1, having values similar to or lower than those for diatomic and atomic colliders. This is in contrast to deactivating collisions, in which polyatomic colliders are in general more effective. The results are discussed in terms of a mechanism in which the NO2 molecules are activated by impulsive collisions creating a distribution of molecules in quantum states above D0 whose populations diminish exponentially with energy. The collisional activation is followed by unimolecular decomposition. The differences between the activation and deactivation pathways are rationalized in terms of the number of degrees of freedom available for energy transfer in each channel.

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