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Anirban Roy

Time Resolved Liquid Jet Photoelectron Spectroscopy
Anirban Roy and Gaurav Kumar


Our group takes advantage of a recently developed technique called time-resolved liquid microjet photoelectron spectroscopy where we use short laser pulses to ionize molecules in a micron diameter liquid beam and detect the outgoing photoelectrons with a multichannel plate after passing through a time-of-flight tube. From the measured flight spectrum we can deduce the underlying energies of the orbitals from where the electrons were kicked out. These orbital energy values have great importance in the determination of redox properties, the interaction between a solute with its solvent (especially with its first solvation shell), and understanding the evolution of chemical reactions if the orbital energy is followed as a function of time.

Because electrons readily scatter within matter, photoelectrons must leave the sample without inelastic scattering and the path to the detector must be in vacuum. Our instrument sits inside a vacuum chamber: powerful turbo-pumps and liquid nitrogen cooled traps provide enough suction and supply a vacuum pressure even lower than outside the International Space Station. By using two laser beams of different colors (wavelength) and varying the (delay) time between the laser pulses we can explicitly follow the ultra-short relaxation processes that occur after excitation, for example bond breakage, isomerization, electron charge transfer or (photo)dissociation.

With this instrument our group focusses on
-exploring the relaxation pathways and photoionization mechanisms of DNA building blocks in water,
-following the evolution of orbitals during charge transfer between transition metal ions and their surrounding ligands and accompanied spin flipping processes

The use of Extreme UV in PE probing

Our goal is to expand the probing window (electron binding energy range) by building a source of extreme UV for both steady-state and transient PE spectroscopy. This advance will enable creation of an energy level diagram for highest occupied orbitals identifying chemical trends across ground state aqueous inorganic systems. Photo-excitation induced changes in occupation, energy and configuration of valence orbitals of any solute can be followed with such a probe. This new capability will be applied in assigning intermediates in the electronic relaxation of transition metals and purines.

Liquid Jet Instrument