Ionization dynamics of acetone and ammonia clusters: Consequences of femtosecond ionization.

摘要

The photochemistry of acetone and acetone clusters upon excitation to energies corresponding to upper regions of the {dollar}rm{lcub}Ssb1,Tsb1{rcub}{dollar} mixed state and the 3s and 3d Rydberg states of the acetone monomer is investigated. These experiments confirm an operative stepwise dissociation mechanism, involving initial loss of a methyl moiety; the excited acetyl further dissociates into CH{dollar}sb3{dollar} and CO. Cleavage of the C-C bond in the acetyl intermediate is dependent upon the internal energy required to exceed the barrier to formation of CO and CH{dollar}sb3{dollar}. Its lifetime is also dependent upon cluster size (solvation).; Also, the role of multiply charged elemental ions as they appear in TOF spectra and in pump-probe experiments are examined. A correlation is drawn between the appearance of multiply charged elemental species in TOF and pump-probe spectra and photodissociation of acetone and acetone clusters. These results support the supposition that clusters are responsible for the formation of ions exhibiting mass spectral patterns consistent with coulomb explosion and concomitant kinetic energy release.; In another investigation, ammonia was chosen as the target molecule to enable study of the effects of hydrogen bonding on the cluster ionization dynamics. Ammonia cluster pump-probe experiments through states corresponding to the C{dollar}spprime{dollar} (or perhaps B) Rydberg state of the ammonia monomer indicate rapid dissociation of the hydrogen bonded species. The observation of unprotonated ammonia cluster ions, (NH{dollar}rmsb3)sb{lcub}n{rcub}sp+{dollar}, in both femtosecond and nanosecond experiments is discussed.; The metastable decay of protonated and unprotonated ammonia cluster ions are investigated via reflectron time-of-flight mass spectrometric techniques. The unprotonated series is found to dissociate microseconds after the ionization event losing an NH{dollar}sb2{dollar} moiety. Metastable dissociation patterns of the protonated ammonia cluster series suggest that fast processes occurring in the resonant intermediate state inhibits complete randomization of energy before initial evaporation of NH{dollar}sb2{dollar} within the ionization region. This hypothesis is supported by kinetic energy release measurements for (NH{dollar}rmsb3)sb{lcub}n{rcub}Hsp+{dollar} (n = 2-9).