Femtosecond ionization and Coulomb explosion of small transition metal carbide clusters

Strong-field ionization and subsequent Coulomb explosion of small group 5 metal carbide clusters are explored using ultrashort pulses centered at 624 nm. More efficient Coulomb explosion was observed according to: Ta > Nb > V due to the larger mass of tantalum, the slower cluster expansion times, and lower ionization potentials of large atoms. Minimum laser intensities required for the onset of each atomic charge state of V, Nb, and Ta were found to be nearly identical between metal carbides and previously observed group 5 metal oxide clusters indicating electron delocalization within the cluster. Ionization enhancement is explored by comparison to semi-classical tunneling theory.