Ultrafast dissociation of the ethyl radical
Alkyl radicals constitute a class of unstable hydrocarbon species with central importance in combustion processes.
Especially the dynamics of the H atom loss and the building of a double bond is of major interest. Amaral et al. investigated
the photodissociation of ethyl measuring the H atom energy-dependent angular distribution after UV excitation of the molecule
and concluded that at least two channels for the dissociation exist . A ‘slow’ channel, which is isotropic in character for H atom
release and therefore is expected to be comparable (or longer) in lifetime to the rotational period (~ ps) and a fast anisotropic
channel with high kinetic energy release, suggesting a prompt and direct dissociation from the excited 2A’(3s) state via
its C2v configuration 2A1(3s).
Figure: Fast and slow dissociation channels of the ethyl radical.
By the application of fs pump - multiphoton-probe spectroscopy on ethyl iodine we observed evidences for the two dissociation
channels of the ethyl radical . The fitted life time of the 3s-Rydberg state is 233 fs at 265 nm excitation
wavelength. A second time constant could be fitted to the detected ion signal to ~ 6-7 ps. This is comparable to the rotational
periods of the molecules. The results confirm the presence of a fast dissociation channel with a dissociation rate in the order
of ~3*1012 s-1 and a ‘slower’ process of ~2*1011 s-1 [3,4].
 G. Amaral, K. Xu, and J. Zhang, J. Chem. Phys., 114 (2001) 5164.
 G. Knopp , P. Beaud, P. Radi, M. Tulej, and T. Gerber,
Femtochemistry and Femtobiology: ultrafast dynamics in molecular science, world scientific,116, (2002)
 W. Hase, B. Schlegel, V. Balbyshev, M. Page, J. Chem. Phys., 100 (1996) 5354.
 A. Zyubin, A. Mebel and S.Lin, Chem. Phys. Lett., 323 (2000) 441.
Figure: Excitation scheme for fs pump multiphoton probe ionization of ethyl iodide. The ion signals
content a fast and a slow decay.