Studies of rapid dynamics in laser-multiphoton ionization dissociation mass spectrometry by using pump-pump two-color picosecond lasers: 2,4-hexadiyne

Photoexcitation, Ionization, and Dissociation of Molecules Using Intense Near-Infrared Radiation of Femtosecond Duration

“…Early investigations by El-Sayed and co-workers demonstrated reduced photodissociation/ionization of molecules using picosecond excitation schemes in comparison with nanosecond excitation. [38][39][40] Reilly and coworkers 41,42 demonstrated that picosecond pulses have higher photoionization yield than nanosecond pulses for molecules with rapid excited-state relaxation. Castleman and co-workers 43 and Gerber and co-workers 44 observed no change in the relative intensities of the ionized molecular and atomic clusters as the power density of a femtosecond duration laser pulse was increased.…”

“…Experimental observation of reduced energy transfer from electronic modes to nuclear modes can be inferred from an increase in ionization probability and a corresponding decrease in the photodissociation probability with decreasing pulse duration of the excitation laser. Early investigations by El-Sayed and co-workers demonstrated reduced photodissociation/ionization of molecules using picosecond excitation schemes in comparison with nanosecond excitation. − Reilly and co-workers , demonstrated that picosecond pulses have higher photoionization yield than nanosecond pulses for molecules with rapid excited-state relaxation. Castleman and co-workers and Gerber and co-workers observed no change in the relative intensities of the ionized molecular and atomic clusters as the power density of a femtosecond duration laser pulse was increased.…”

Formation of chlorophenyl (C6H4Cl+) ions by laser multiphoton ionization-fragmentation of 1,3-dichlorobenzene using the two-color picosecond mass spectrometric technique

“…As depicted in Figure 2, the C6H4C1+ ion yield curve as a function of delay time is very sensitive to the visible pulse intensity. The important results can be summarized as follows: (1) At low green power (curve c), the C6H4C1+ ion signal increases at zero delay and then slowly decreases as the deláy time increases. (2) At high green laser power (curve a), a spike in the daughter ion is observed at zero delay.…”

Multiphoton ionization and chemical dynamics

“…In addition, many ionization schemes require tunable near-utraviolet radiation so that appropriate nonlinear mixing crystals and/or Raman shifting cells are required. More recent studies have taken MPI spectroscopy into the faster time regime employing both picosecond (for example Gobeli et al (1984), Tai and El-Sayed (1986), Szaflarski and El-Sayed (1988), Beuerman and Stuke (1989 and DeBoer and Muller (1992)) and femtosecond (for example Baumert et al (1990( ), Dantus et al (1991 and Wei et al (1992)) laser pulses. The picosecond time frame generally promotes the formation of molecular ions over fragment ions, a decided advantage in yield being of importance to measurements of molecular ion decomposition.…”

“…An alternative technique based upon the reflection TOF mass spectrometer allows for pump-probe interrogation of the ion formation rate (Gobeli et al 1985), a pulsedexcitation pulsed-extraction study of rate constants El-Sayed 1986) or a determination of the rate at which initial excitation energy is redistributed prior to fragmentation (Gobeli et al 1984), depending upon the exact experimental arrangement. In the latter experiment the technique, using picosecond lasers and a linear TOF spectrometer, was employed in the first attempt to study directly the redistribution of energy in 2,4-hexadiyne.…”