Is there anybody out there? Ultrafast Rydberg–valence interactions in the photodissociation of trimethylamine
Abstract
Trimethylamine (TMA) is a tertiary aliphatic amine that stands as a potential marker for life beyond Earth due to only being naturally produced via biotic means. However, its propensity to undergo photodissociation in the gas phase when excited by a deep ultraviolet photon means that its amine daughter product could serve as an additional biomarker and confirmational spectral signature of TMA in exoplanetary atmospheres. The photochemistry of TMA is dominated by strong Rydberg–valence state interactions. To understand how these interactions lead to its amine photoproduct, we employ time-resolved extreme ultraviolet photoelectron spectroscopy where TMA is pumped by a 200 nm femtosecond laser pulse and analyze the results with the help of electronic structure calculations of the excited state potential energy surface relevant to the process. Our combined experimental and theoretical study indicates that from the decay of the initially prepared 3pz state (time-constant 400 fs), internal conversion through the remaining 3p manifold (4.4 ps) and the 3s state (67 ps) states competes with ultrafast photodissociation, forming ground state dimethyl amidogen (DMA) and CH3 (ν2 = 4) radical products. Decay of the 3s state reveals the formation of a second product pair, forming DMA in a low-lying excited state, DMA (Ã2A1), and vibrationally cold CH3. We suggest that the rapid dissociation channel arises from a near-planar geometry accessed in the 3pz state and the longer time channel arises from the excited state population, accessing a pyramidal geometry in the 3s state.
Article Details
Journal Info
The Journal of Chemical Physics
American Institute of Physics
Authors (15)
Derri J. Hughes
School of Chemistry and Chemical Engineering, University of Southampton 1 , University Road, Highfield, Southampton SO17 1BJ,
Andrew W. Prentice
School of Engineering and Physical Sciences, Heriot-Watt University 2 , Edinburgh EH14 4AS,
Lauren Bertram
Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford 3 , South Parks Road, Oxford,
Richard T. Chapman
Central Laser Facility, STFC Rutherford Appleton Laboratory 4 , Didcot, Oxfordshire OX11 0QX,
Luca Craciunescu
Institute of Chemical Sciences, School of Engineering and Physical Sciences, Heriot-Watt University , Edinburgh EH14 4AS,
Daniel A. Horke
Institute for Molecules and Materials, Radboud University 4 , Heijendaalseweg 135, 6525 AJ Nijmegen,
Peter Krüger
Institute for Molecules and Materials, Radboud University 5 , Heijendaalseweg 135, 6525 AJ Nijmegen,
Michael A. Parkes
Department of Chemistry, University College London 6 , 20 Gordon Street, London WC1H 0AJ,
Henry J. Thompson
School of Chemistry and Chemical Engineering
Emma Springate
Central Laser Facility, STFC Rutherford Appleton Laboratory 4 , Didcot, Oxfordshire OX11 0QX,
James O. F. Thompson
Central Laser Facility, STFC Rutherford Appleton Laboratory 4 , Didcot, Oxfordshire OX11 0QX,
Yu Zhang
Xiangya Hospital, Central South University Changsha China
Adam Kirrander
Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford 16 , Oxford OX1 3QZ,
Martin J. Paterson
Institute of Chemical Sciences, School of Engineering and Physical Sciences, Heriot-Watt University , Edinburgh EH14 4AS,
Russell S. Minns
School of Chemistry and Chemical Engineering