Dynamics of Gas-Liquid Reactions; The Pseudo-Surface Approach
Lead Research Organisation:
Heriot-Watt University
Department Name: Sch of Engineering and Physical Science
Abstract
Chemical reactions require a collision between two chemical species, and have been widely developed and exploited in solution by synthetic chemists to make a variety of products such as plastics and drugs. Chemical interactions are studied in greater detail by physical chemists, who often work with gases in order to isolate individual molecular collisions for quantitative study. However the fundamental dynamics of dual-phase (gas-liquid) interactions are poorly understood and, to date, have received only limited attention. Gas-liquid interactions are of particular importance to a wide variety of physical processes, ranging from respiration in living organisms (which relies on uptake of oxygen from air, into the blood) to distillation, gas chromatography, and atmospheric chemistry at the surfaces of aerosol particles (where for example water droplets in air can absorb sulfuric acid to from acid rain) and the Earth's oceans.
The aim of the proposed research is to improve the fundamental understanding of gas-liquid surface interactions by employing a novel experimental strategy; using a large, but volatile, flexible molecule as a simplified proxy for a liquid surface (a pseudo-surface). This will allow chemical reactions that occur at the gas-liquid interface to be studied in unprecedented detail using high resolution laser based techniques coupled with imaging methods. The imaging allows pictures to be taken of the fate of products of a chemical reaction, which will allow us to develop in-depth understanding of the mechanisms involved.
This project will focus on the construction and use of a unique, compact imaging experiment that will be the first of its kind in the UK. Using the experiment we can measure the direction and speed with which any products of reactions fly. This will allow us to gain in-depth knowledge of the different possible reaction mechanisms of collisions of molecules with pseudo-surfaces. The simplest pathway is a single collision reaction, called a direct mechanism. Some colliding atoms or molecules are trapped on the surface, however, undergoing multiple collisions before reacting (a so called trapping-desorption mechanism), and in extreme cases the pseudo-surface adsorbs the other reagent. The football / apple tree analogy is helpful here: imagine if you kick a football into an apple tree, it could come out straight away, bouncing off a branch, bringing an apple with it (direct mechanism), or it could get temporarily caught bouncing from branch to branch before leaving with an apple (trapping-desorption), or it could become wedged between the branches. The work proposed here will study the football and apple tree problem in detail and use it as a model to investigate the football and orchard problem (the real liquid, where lots of identical molecules (apple trees) make up the surface). This analogy can be extended to use rugby and other shaped balls to represent different incoming atoms/molecules/radicals that we intend to study.
The research will have a profound impact on the understanding of surface interactions, and will be of benefit to a broad community of researchers in Chemistry, Physics, Engineering, and ultimately Life Sciences, with interest in gas-liquid interfaces.
The aim of the proposed research is to improve the fundamental understanding of gas-liquid surface interactions by employing a novel experimental strategy; using a large, but volatile, flexible molecule as a simplified proxy for a liquid surface (a pseudo-surface). This will allow chemical reactions that occur at the gas-liquid interface to be studied in unprecedented detail using high resolution laser based techniques coupled with imaging methods. The imaging allows pictures to be taken of the fate of products of a chemical reaction, which will allow us to develop in-depth understanding of the mechanisms involved.
This project will focus on the construction and use of a unique, compact imaging experiment that will be the first of its kind in the UK. Using the experiment we can measure the direction and speed with which any products of reactions fly. This will allow us to gain in-depth knowledge of the different possible reaction mechanisms of collisions of molecules with pseudo-surfaces. The simplest pathway is a single collision reaction, called a direct mechanism. Some colliding atoms or molecules are trapped on the surface, however, undergoing multiple collisions before reacting (a so called trapping-desorption mechanism), and in extreme cases the pseudo-surface adsorbs the other reagent. The football / apple tree analogy is helpful here: imagine if you kick a football into an apple tree, it could come out straight away, bouncing off a branch, bringing an apple with it (direct mechanism), or it could get temporarily caught bouncing from branch to branch before leaving with an apple (trapping-desorption), or it could become wedged between the branches. The work proposed here will study the football and apple tree problem in detail and use it as a model to investigate the football and orchard problem (the real liquid, where lots of identical molecules (apple trees) make up the surface). This analogy can be extended to use rugby and other shaped balls to represent different incoming atoms/molecules/radicals that we intend to study.
The research will have a profound impact on the understanding of surface interactions, and will be of benefit to a broad community of researchers in Chemistry, Physics, Engineering, and ultimately Life Sciences, with interest in gas-liquid interfaces.
Planned Impact
The initial impact of the proposed research will mainly be in the academic community where the new approach of pseudo-surface scattering will enhance the study of gas-liquid scattering processes, bringing new insights into the detail of the mechanisms of scattering processes. Experimental advances will open a new chapter in the study of gas-liquid interactions by allowing 'real world' surfaces such as water to be used in these studies. This will, in the longer term allow the study of important gas-liquid processes that are present in: distillation, gas chromatography, respiration in living organisms, atmospheric chemistry at the surfaces of aerosol particles and the Earth's oceans, and other such technological, biological and environmental applications.
The project will provide high quality training for a PhD student, and further skills and career development opportunities for two research associates, enhancing the skills of the Uk workforce.
The project will provide high quality training for a PhD student, and further skills and career development opportunities for two research associates, enhancing the skills of the Uk workforce.
People |
ORCID iD |
| Stuart Greaves (Principal Investigator / Fellow) |
Publications
Dunning GT
(2015)
Vibrational Excitation of Both Products of the Reaction of CN Radicals with Acetone in Solution.
in The journal of physical chemistry. A
Dunning GT
(2014)
Dynamics of photodissociation of XeF2 in organic solvents.
in Physical chemistry chemical physics : PCCP
Dunning GT
(2015)
Reaction dynamics. Vibrational relaxation and microsolvation of DF after F-atom reactions in polar solvents.
in Science (New York, N.Y.)
Hadden DJ
(2016)
Note: Velocity map imaging the scattering plane of gas surface collisions.
in The Review of scientific instruments
Tkác O
(2014)
Differential and integral cross sections for the rotationally inelastic scattering of methyl radicals with H2 and D2.
in The Journal of chemical physics
Tkác O
(2013)
Rotationally inelastic scattering of CD3 and CH3 with He: comparison of velocity map-imaging data with quantum scattering calculations
in Chemical Science
| Description | The most significant discovery is that, counterintuitively, the environment where a chemical reaction is taking place does not affect the immediate outcome of the reaction. For example it is known that in an isolated exothermic reaction (one that gives out energy) the products of the reaction are formed in an excited state; that is they are vibrating and rotating much more than the same molecules in a relaxed state. It was widely assumed that when such reactions happen in solution that this excess energy is instantly removed by the solvent. Our experiments have shown that in the immediate aftermath of reaction the higher levels of vibration and rotation are still present for some time before the solvent can remove the excess energy. This means that many important results and observations from highly detailed gas-phase work on chemical dynamics (e.g. Polyani's rules) are still applicable to 'normal' chemistry, i.e. reactions in solution. New research methods were developed to enable the use of the key gas phase chemical dynamics tool velocity map ion imaging in systems investigating gas-surface dynamics. This multiplexing technique will allow more detailed future study of gas-surface phenomena that could have relevance in many areas of science and industry. |
| Exploitation Route | The findings will be taken forward by the chemical dynamics research community. The work on solution phase dynamics has been particularly popular with the community inspiring several other groups to pursue work, both experimentally and theoretically in this area. The applicability of these results to reaction in solution will also be of use to synthetic chemists looking for detailed knowledge of reaction mechanisms to apply to optimize synthetic pathways. The new experimental methodologies developed to investigate gas-surface scattering have clear advantages over the current widely used technologies, so I would expect them to be adopted by the research groups in this field. |
| Sectors | Chemicals,Environment,Other |
| Description | The PhD student trained on this grant is now employed within the UK scientific industry and thus able to contribute to the economic competitiveness of the UK. |
| First Year Of Impact | 2017 |
| Sector | Chemicals,Manufacturing, including Industrial Biotechology |
| Impact Types | Economic |