Collisional Energy Transfer in Biomolecular Ion- Molecule Dynamics
Abstract
Guided ion beam kinetic energy thresholds in the ion-molecule reactions M(+) + H2 yields M H(+) + H where M(+) = B(+), Al(+), and Ga(+) exceed by 0.4 to ca. 5 eV the thermodynamic energy requirements or theoretically computed barrier heights of these reactions. In addition, the formation of MD(+) occurs at a significantly lower threshold than MH(+) when M(+) reacts with HD. Moreover, the measured reaction cross sections for production of MH(+) productions are very small (10(exp-17) to 10(exp-20) sq cm.). These facts suggest that a dynamical bottleneck' may be operative in these reactions. In this work, the eigenvalues of the mass-weighted Hessian matrix, which provide local normal mode frequencies are used to identify locations on the ground-state MH2(+) potential energy surfaces where collisional to internal energy transfer can readily take place. In particular, the potential energies at geometries where eigenvalues corresponding to inter-fragment and to internal motions undergo avoided crossings are related to the kinetic energies of apparent reaction thresholds. This near resonance energy transfer model, applied to M(+) + HD reactions, displays the experimentally observed preference to form MD(+) at lower collision energies than MH(+) as well as the fact that reaction thresholds may greatly exceed thermodynamic energy requirements.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 25, 1993
- Accession Number
- ADA260911
Entities
People
- Jack Simons Ii
- Jon Ru
- Maciej Gutowski
- Mark Roberson
Organizations
- University of Utah