The wavelength dependence of the electronic dephasing time in the optically excited state of the NO dimer has been measured by femtosecond pump-probe photoelectron imaging for the range of 200-235 nm. The observed dephasing time increased from 0.2 to 1 ps towards longer photoexcitation wavelengths. The 3s Rydberg state was formed with similar time constants for excitation wavelengths of lambda < 220 nm. (C) 2003 Elsevier B.V. All rights reserved.