“…A more extended overview of experimental methods to produce tunable IR radiation for the spectroscopy of transient gas-phase species has been given by Bernath. 115 However, other IR lasers like the molecular CO or far-IR lasers, as well as lead-salt, F-center, or quantum-cascade lasers are less frequently applied in studies of metal cluster complexes, mostly due to their low (peak) powers and limited tunability. This holds also for frequency conversion via mixing with microwave radiation or by harmonics generation, i.e., for shifting the output of a CO 2 laser into the region around 5 mm (2000 cm À1 ).…”