Energy partitioning in polyatomic chemical reactions: Quantum state resolved studies of highly exothermic atom abstraction reactions from molecules in the gas phase and at the gas-liquid interface

2009 2009

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Abstract (summary)

This thesis recounts a series of experiments that interrogate the dynamics of elementary chemical reactions using quantum state resolved measurements of gas-phase products. The gas-phase reactions F + HCl → HF + Cl and F + H2O → HF + OH are studied using crossed supersonic jets under single collision conditions. Infrared (IR) laser absorption probes HF product with near shot-noise limited sensitivity and high resolution, capable of resolving rovibrational states and Doppler lineshapes. Both reactions yield inverted vibrational populations. For the HCl reaction, strongly bimodal rotational distributions are observed, suggesting microscopic branching of the reaction mechanism. Alternatively, such structure may result from a quantum-resonance mediated reaction similar to those found in the well-characterized F + HD system. For the H2O reaction, a small, but significant, branching into v = 2 is particularly remarkable because this manifold is accessible only via the additional center of mass collision energy in the crossed jets. Rotationally hyperthermal HF is also observed. Ab initio calculations of the transition state geometry suggest mechanisms for both rotational and vibrational excitation.

Exothermic chemical reaction dynamics at the gas-liquid interface have been investigated by colliding a supersonic jet of F atoms with liquid squalane (C30H62), a low vapor pressure hydrocarbon compatible with the high vacuum environment. IR spectroscopy provides absolute HF( v,J) product densities and Doppler resolved velocity component distributions perpendicular to the surface normal. Compared to analogous gas-phase F + hydrocarbon reactions, the liquid surface is a more effective "heat sink," yet vibrationally excited populations reveal incomplete thermal accommodation with the surface. Non-Boltzmann J-state populations and hot Doppler lineshapes that broaden with HF excitation indicate two competing scattering mechanisms: (i) a direct reactive scattering channel, whereby newly formed molecules leave the surface without equilibrating, and (ii) a partially accommodated fraction that shares vibrational, rotational, and translational energy with the liquid surface before returning to the gas phase.

Finally, a velocity map ion imaging apparatus has been implemented to investigate reaction dynamics in crossed molecular beams. Resonantly enhanced multiphoton ionization (REMPI) results in rotational, vibrational, and electronic state selectivity. Velocity map imaging measurements provide differential cross sections and information about the internal energy distribution of the undetected collision partner.

Indexing (details)

Physical chemistry;
Molecular physics
0494: Physical chemistry
0609: Molecular physics
Identifier / keyword
Pure sciences; Chemical dynamics; Infrared spectroscopy; Interfacial dynamics; Quantum state resolved; Reaction dynamics; Reactive scattering
Energy partitioning in polyatomic chemical reactions: Quantum state resolved studies of highly exothermic atom abstraction reactions from molecules in the gas phase and at the gas-liquid interface
Zolot, Alexander M.
Number of pages
Publication year
Degree date
School code
DAI-B 70/07, Dissertation Abstracts International
Place of publication
Ann Arbor
Country of publication
United States
Nesbitt, David J.
Committee member
Cornell, E. A.; Greene, C. H.; Lineberger, W. C.; Weber, J. M.
University of Colorado at Boulder
University location
United States -- Colorado
Source type
Dissertations & Theses
Document type
Dissertation/thesis number
ProQuest document ID
Database copyright ProQuest LLC; ProQuest does not claim copyright in the individual underlying works.
Document URL
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