IR multiple-photon excitation of polyatomic molecules: a route towards nanostructures

The availability of high power IR laser sources in the 1980s paved the way to new attractive experiments for driving chemical reactions, based on the selective excitation of vibrational modes in polyatomic molecules up to and above the dissociation threshold. The process was first studied in the collisionless regime for applications to laser isotope separation and selective chemistry, and later in collision-assisted conditions leading to the synthesis of nanostructures. In particular, the mechanisms of IR laser pyrolysis of SiH4 and hydrocarbons were investigated in order to control the production of silicon- and carbon-based nanoaggregates. For this purpose, different on-line diagnostics were utilized to monitor the gas-phase reaction intermediates and the process of particle nucleation and growth. The basic principles of the process of multiple-photon excitation of polyatomic molecules and its applications to the synthesis of nanostructures will be reviewed in this paper. Peculiar optical properties of silicon nanoparticles and carbon nanotubes obtained as final products of the developed processes will be described in relation to remarkable applications in several fields.