¹B₂(¹Σ_u⁺) excited state decay dynamics in CS₂

The authors report time resolved photoelectron spectra of the B-1(2)((1)Sigma(+)(u)) state of CS2 at pump wavelengths in the region of 200 nm. In contrast to previous studies, the authors find that the predissociation dynamics is not well described by a single exponential decay. Biexponential modeling of the authors' data reveals a rapid decay pathway (tau < 50 fs), in addition to a longer lived channel (tau similar to 350-650 fs) that displays a marked change in apparent lifetime when the polarization of the pump laser is rotated with respect to that of the probe. Since the initially populated B-1(2)((1)Sigma(+)(u)) state may decay to form either S(D-1) or S(P-3) products (the latter produced via a spin-orbit induced crossing from a singlet to a triplet electronic surface), this lifetime observation may be rationalized in terms of changes in the relative ionization cross section of these singlet and triplet states of CS2 as a function of laser polarization geometry. The experimentally observed lifetime of the longer lived channel is therefore a superposition of these two pathways, both of which decay on very similar time scales. (c) 2006 American Institute of Physics.