The Chilli-jet

Chilli - Chemical imaging by spatially resolved infrared spectroscopy

The chilli-jet enables the space-resolved (2D), synchronous recording of FTIR spectra of supersonic expansions with a focal plane array (FPA) detector. Compared to mapping techniques, this area detector allows for a considerable reduction of recording times and substance consumption, as well as better reproducibility. The detector array consists of 64 x 64 detector elements (pixels), each 40 x 40 μm2 in size. An IR lens with a fourfold demagnification provides a 1 x 1 cm2 field of view of the expansion. The spatial resolution achieved is better than 0.4 mm (further limited by data pre-processing; for details see [129]).

Continuous or pulsed expansions of the gaseous sample seeded in helium are performed through a slit nozzle into a vacuum chamber (<2 mbar). In order to study cluster stability in shock waves, a custom double slit nozzle was designed in addition to the single slit nozzle used to study the aggregation behaviour of clusters [159].

2D visualisations (“chemical images”) of the cluster formation and decomposition in supersonic expansions are obtained by integrating over the monomer or cluster band of interest, as exemplarily shown for the formic acid dimer band in the figure below.

sample data from the chilli-jet
Chemical image of the formic acid dimer in a helium jet expansion (blue = low intensity, red = high intensity, black = single slit nozzle). On the right-hand side, a spectrum averaged over 8 x 8 pixel is shown (shaded area = dimer band integral).

Current projects

  • Study of aggregation behaviour of carboxylic acids as well as their cluster stability in shock waves (including hetero dimers with and without amides)
  • Design of new double slit nozzles to study reactive processes
  • Extension of the spectral range