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Coherent Phase Control of Internal Conversion in Pyrazine
- Publication Year :
- 2014
-
Abstract
- Shaped ultrafast laser pulses were used to study and control the ionization dynamics of electronically excited pyrazine in a pump and probe experiment. For pump pulses created without feedback from the product signal, the ion growth curve (the parent ion signal as a function of pump/probe delay) was described quantitatively by the classical rate equations for internal conversion of the $S_2$ and $S_1$ states. Very different, non-classical behavior was observed when a genetic algorithm (GA) was used to minimize the ion signal at some pre-determined target time, T. Two qualitatively different control mechanisms were identified for early (T$<1.5$ ps) and late (T$>1.5$ ps) target times. In the former case, the ion signal was largely suppressed for $t<T$, while for $t \gg T$ the ion signal produced by the GA-optimized pulse and a transform limited (TL) pulse coalesced. In contrast, for $T>1.5$ ps the ion growth curve followed the classical rate equations for $t<T$, while for $t \gg T$ the quantum yield for the GA-optimized pulse was much smaller than for a TL pulse. We interpret the first type of behavior as an indication that the wave packet produced by the pump laser is localized in a region of the $S_2$ potential energy surface where the vertical ionization energy exceeds the probe photon energy, whereas the second type of behavior may be described by a reduced absorption cross section for $S_0 \rightarrow S_2$ followed by incoherent decay of the excited molecules.
- Subjects :
- Physics - Atomic Physics
Subjects
Details
- Database :
- arXiv
- Publication Type :
- Report
- Accession number :
- edsarx.1409.6360
- Document Type :
- Working Paper
- Full Text :
- https://doi.org/10.1063/1.4916642