Chemical Reaction Dynamics by the Crossed Molecular Beam Technique

Principal Investigators: Prof. Piergiorgio Casavecchia and Prof. Nadia Balucani

Dipartimento di Chimica - Universita' degli Studi di Perugia - Via Elce di Sotto, 8 - 06123 PERUGIA - ITALY
Fax: + 39 075 585 5606    Telephone: + 39 075 585 5514 / 5507 / 5513

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RESEARCH ACTIVITY

Our main research activity is in the field of chemical reaction dynamics. We use the crossed molecular beam (CMB) scattering technique with rotating mass spectrometric detection and time-of-flight analysis to measure reactive differential cross sections for elementary chemical reactions of importance from a fundamental point of view and in areas of practical interest, such as atmospheric-, combustion- and astro-chemistry. The main thrust of our CMB work during the last years has been that of:

  • investigating the reactive scattering of oxygen atoms with special focus on electronically excited O( 1D) and on the comparative study of O(3P) and O(1 D) reaction dynamics;

  • investigating the  reactive scattering of nitrogen atoms;

  • providing scattering data for the benchmark chlorine atom reaction Cl+H2(D2);

  • studying the dynamics of simple, prototypical insertion reactions such as O(1D)+H2, C(1D)+H2 and N(2D)+H2  to provide experimental data for comparison with theory;

  • extending reactive scattering studies to the chemically very important hydroxyl radical, by studying the benchmark reactions OH+H2 and OH+CO;

  • exploring the reactive scattering of O and Cl atoms from a liquid hydrocarbon surface (in coll. with T.K. Minton, Montana State University);

  • exploring the reactive scattering of carbon atoms, both ground state C(3P) and excited state C(1D), with hydrocarbons;

  • exploring the reactive scattering of cyano (CN) and dicarbon (C2) radicals with unsaturated hydrocarbons;

  • extending reactive scattering studies to radical-radical reactions such as O-atoms with hydrocarbon radicals;

  • extending reactive scattering studies to sulfur atoms,

The experimental results are often compared with those of dynamical calculations, both by quantum mechanical and quasiclassical trajectory methods, on the relevant potential energy surfaces within international collaborations with leading theoretical groups.

Recently, we have made significant advances in the investigation of the dynamics of elementary reactions by the CMB method, following the following key improvements of the CMB apparatus:

(a) soft electron-ionization, to reduce interfering signals originating from dissociative ionization processes, usually representing a major complication;

(b) different beam crossing-angle set-ups, to extend the range of collision energies over which a reaction can be studied;

In addition, we have recently developed continuous supersonic beam sources of new atomic and molecular radical reactant beams. Besides C, N, O, and Cl atoms and OH radicals, also beams of Sulfur atoms and CN, C2, CH3, and C3H5 (allyl) radicals have been implemented.  

These improvements have permitted us to tackle the detailed dynamics of:

  • polyatomic multichannel radical-molecule reactions

  • radical-radical reactions

by identifying all the primary products, characterizing their formation dynamics, and determining the branching ratios. A recent Perspective article (PCCP 2009) demonstrate that the type of dynamical results now obtainable on polyatomic multichannel radical-molecule and radical-radical reactions might well complement reaction kinetics experiments and hence contribute to bridging the gap between microscopic reaction dynamics and thermal reaction kinetics, enhancing significantly our basic knowledge of chemical reactivity and understanding of the elementary reactions which occur in real-world environments, from combustion to interstellar and planetary atmosphere chemistry.

Very recently, we have also set-up a crossed laser-radical beam apparatus in a new laboratory in which we use Laser-Induced-Fluorescence (LIF) and Resonant-Enhanced-Multiphoton-Ionization (REMPI) to probe and characterize in their internal (electronic and ro-vibrational) quantum states the supersonic radical beams to be used in CMB reactive scattering studies.

The investigation of the dynamics of polyatomic multichannel reactions and radical-radical reactions is our major current effort.

 

To learn more about these topics, visit the following pages:

  • Experimental details: 

- Crossed Beam Machine (schematic, photos)

- Soft electron-ionization (EI) detection

- Variable beam crossing angle set-ups (γ = 45o, 90o, 135o)

- Continuous supersonic radical beam sources (RF discharge and flash-pyrolysis)

- LIF Machine (photograph)