Photoionization of atomic and molecular clusters doped with low ionization energy molecules: Effect of laser wavelength, intensity and cluster composition

摘要

Photoionization of (Ar)_l, (Xe)_m, (SF _6)_n and (Xe)_m (SF6)_n cluster systems, each doped with Fe(CO)_5, has been studied at selected laser wavelength ranging from UV to IR region using time-of-flight mass spectrometer (TOFMS). In addition to TOFMS studies, charge density measurements were carried out to quantify the total ion yield generated during the laser-cluster interaction studies. In the first set of experiments, doped clusters of identical composition were irradiated with laser pulses of different wavelength. In this case the charge state of atomic ions was observed to increase with increasing laser wavelength while the total ion yield was found to decrease. Results obtained in the present study have been rationalized on the basis of the expansion dynamics of charged clusters which depends on the number of charge centers generated during initial multiphoton ionization step as well as on the binding energy of cluster constituents. In the second set of experiments, clusters of different composition were irradiated with laser pulses of identical wavelength and intensity. In this case doped molecular clusters were observed to interact more efficiently with optical pulses as compared to doped atomic clusters. This was attributed to higher binding energy of the constituents within the doped molecular clusters which reduces the rate of expansion of charged clusters thereby enhancing the efficiency of laser-cluster interaction.