The ionization rate of several linear polyenes subjected to short, intense laser pulses was simulated using the time dependent single-excitation configuration-interaction (TD-CIS) method, and Klamroth's heuristic model for ionization.  Ionization rates were calculated as a function of the number of excited states, basis set size, ionization distance parameter, and field strength.  The calculations used the 6-31G(d,p) basis set augmented with up to 3 sets of diffuse sp functions on each heavy atom as well as the 6-311++G(2df,2pd) basis set.  The TD-CI simulations were carried out with a 7 cycle cosine pulse (?=0.06 au, 760 nm) with intensities up to 3.51�1014 W cm-2 directed along the vector connecting the end carbons of the linear polyenes.  As the length of the polyene chain increases the ionization potential of the molecule decreases and similarly the ionization rate should increase as a function of chain length.  The heuristic model developed by Klamroth et al (J. Chem. Phys. 2009 , 131(11), 114304), faithfully reproduces this trend, producing ionization saturation values for each of the polyenes (ethylene, butadiene, hexatriene, octatetraene) in qualitative agreement with values available experimentally.  Ionization of the polyenes was found to be largely independent of basis set size, and in contrast to earlier non-ionizing simulations, only a fraction of the total possible CIS states are needed to accurately model the strong field ionization.

TD-CI simulation of the strong field ionization of polyenes

243rd National Meeting (2012)

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