We build and operate custom, ultrahigh vacuum mass spectrometry and ion spectroscopy and tunable laser systems
to study isolated molecules with high temporal and spatial resolution. Our instruments (two maininstruments, and one
under slow construction) are descibed on the Instruments page.
Ultrafast dynamics of chromophores and the impact of solvation
Timescales of the dynamic processes relevant in photophysics of gas-phase ions,
spanning the femto- to microsecond range. Also shown are laser pulse durations; the
femtosecond laser pulse (blue) has a precise duration (narrow) but consists of a broader range of
wavelengths, and vice versa for the nanosecond laser pulse (green). Note that the time scale is broken
in the nanosecond to microsecond range. The two processes in grey are specific to solution and
modify the importance or occurrence of slower dynamics in solution compared with the gas phase.
Chromophores are light-absorbing molecules, with common examples including aromatic groups, dyes, and highly conjugated molecules. Biochromophores
are the light-absorbing units in biomolecules, with examples including fluorescent protein chromophores (e.g. green fluorecent protein),
Isomer-specific spectroscopy and photoisomerisation dynamics
2D photoelectron-photodetachment spectroscopy of temporary anion and non-valence states
Velocity-map imaging
Schematic illustration of a simple three electrode velocity-map imaging stack. R = repeller, E = extractor, G = ground.
PAHs and carbonaceous molecules in space; radiative stabilisation mechanisms
Schematic illustration of DIBs (diffuse interstellar bands) and AIBs (aromatic infrared bands). These absorption (DIB) and emisison (AIB)
features are observed across various regions of space and originate from electronic and vibrational transitions in isolated molecules. The AIBs are widespread
from interstellar regions such as TMC-1.
Polycyclic aromatic hydrocarbon (PAH) molecules are thought to be one of the major sources of carbon in space.
This hypothesis is based on widespread observations of UIBs (unidentified infrared bands), which are now largely accepted as AIBs (aromatic infrared bands)
as they resemble infrared (IR) spectra for aromatic and PAH molecules. Recently, the deployment of the James Webb space telescope, which observes in the IR,
is highlighting the widespread abundance of IR emitters in space. With Dr Mark Stockett at Stockholm University, we are interested in
studying the underlying physics and chemistry of PAHs and other carbonaceous molecules that have been identified in space through radioastronomy and likely unidentified candidates.
Quantum chemical calculations and ab initio molecular dynamics to support experiments
Gas-phase experiments provide reference data to calibrate and benchmark computational chemistry methods. When deviation exists, the experiments then provide direction for the refinement of theory.
We use a variety of electronic struture methods to help interpret and assign our measurements. Often,
our measurements provide fundmamental references for the calibration of theoretical methods. There is always a balance between computational cost
and accuracy of the calculation that needs to be considered. While DFT is becoming very common and attractive due to computational cost (particuarly in the TD-DFT framework)
it can often provide a non-physical description.
