IR-REMPI of vanadium-carbide nanocrystals: Ideal versus truncated lattices

Neutral vanadium-carbide clusters are produced in the gas phase with laser vaporization in a pulsed nozzle source and excited with a free electron laser in the 400–1000 cm−1 region. Resonant multiphoton excitation induces thermionic electron emission in the isolated metal carbide nanocrystals. This process only occurs for stable neutral clusters which resist multiphoton dissociation. The species observed are cubic nanocrystals and truncated nanocrystals with carbon vacancies at their corners. Their wavelength spectra exhibit resonances associated with surface phonons. The resonance shows only a weak size dependence, shifting from 530 to 490 cm−1 in going from V14C12 to V32C32.