Femtisecond single-mole infrared spectroscopy of molecular clusters.

The sensitivity limitations of Fourier transform infrared (FTIR) spectroscopy for the detection of molecular clusters formed in rarefied gas expansions can be overcome by synchronizing intense gas pulses at a low duty cycle with rapid interferometer scans. This turns the broadband FTIR approach into a universal cluster spectroscopy tool applicable from the far (200 cm(-1)) to the near (8000 cm(-1)) IR. It nicely complements more selective and more restricted laser-based techniques and it provides a gas-phase variant of the matrix-isolation method, the main drawback being substance consumption. A survey over the capabilities, limitations and perspectives of this high-throughput nozzle approach to cluster FTIR spectroscopy is given.