Project

Back to overview

Characterization of Vibrationally and Rotationally Excited Molecules by Two-Color Resonant Four-Wave Mixing

English title Characterization of Vibrationally and Rotationally Excited Molecules by Two-Color Resonant Four-Wave Mixing
Applicant Radi Peter
Number 115958
Funding scheme Project funding (Div. I-III)
Research institution Paul Scherrer Institut
Institution of higher education Paul Scherrer Institute - PSI
Main discipline Physical Chemistry
Start/End 01.04.2007 - 31.12.2008
Approved amount 97'644.00
Show all

Keywords (11)

non-linear spectroscopy; two-color resonant four-wave mixing; formaldehyde; transition state; excited molecules; unimolecular dissociation; elementary reactions; PHOFEX; double-resonance; molecular beam; discharge source

Lay Summary (English)

Lead
Lay summary
Combustion modeling of trace pollutants, soot formation, heat release, ignition delays and so on requires chemical mechanisms with such large number of reactions that the thermo-chemistry and kinetics cannot be determined experimentally but must be mostly calculated. Many useful ways are available by using extensive empirical correlations. However, for a more complete understanding of the underlying elementary reactions, including highly reactive, unstable species exhibiting substantial internal energy, extended methods of experimental and theoretical chemistry are required.

This research project applies specially designed spectroscopic techniques to the investigation of the relevant elementary reactions. In particular, the dynamics of vibrationally and rotationally excited molecules on both, the ground and excited state potential energy surface are characterized. For example, experiments are performed that shed light on the statistical/non-statistical behavior of the unimolecular dissociation process of formaldehyde (H2CO -> H + HCO) by applying photo-fragment excitation spectroscopy. The experiment involves preparation of formaldehyde in the well-defined, collision-less environment of a molecular beam. By applying degenerate four-wave mixing, a relatively novel non-linear spectroscopic technique, parent molecules are excited to well defined quantum states above the dissociation threshold. Subsequently, the unimolecular dissociation product HCO is state-selectively detected by using laser-induced fluorescence. The method provides highly sensitive, state-to-state photo-fragmentation quantum yields containing important dynamic information on the unimolecular dissociation process.

Statistical theories are applied to model the fragment yields. PRIOR is the simplest theory and assumes the absence of any dynamical bias. All energetically allowed final product states are formed with the same rate. The relative quantum yield is then obtained by counting the possible quantum states of HCO at the given energy. The deviation of the observed quantum yields from the PRIOR calculations measures the importance of dynamics in the dissociation process. The constraints imposed by dynamical effects are modeled by Phase Space Theory and the Statistical Adiabatic Channel Model. However, strong propensities are observed that are difficult to model by statistical theories and a comprehensive study by sophisticated ab initio computations is required.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Associated projects

Number Title Start Funding scheme
105118 Characterization of Vibrationally and Rotationally Excited Molecules by Two-Color Resonant Four-Wave Mixing 01.01.2005 Project funding (Div. I-III)
124542 Spectroscopic Characterization of Radicals by Degenerate and Two-Color Resonant Four-Wave Mixing 01.01.2010 Project funding (Div. I-III)
175490 Mapping the electronic structure of transition metal dimers by degenerate and two-color four-wave mixing 01.10.2017 Project funding (Div. I-III)
124542 Spectroscopic Characterization of Radicals by Degenerate and Two-Color Resonant Four-Wave Mixing 01.01.2010 Project funding (Div. I-III)

-