The excited-mate lifetime of the 2,3-dimethylbut-2-yl (DMB) radical, it hexyl isomer, upon electronic excitation into the 3p Rydberg state at 265 nm, is measured by femtosecond time-resolved photoionization. It is shown that the 3p state deactivates in I two-step process, which is well described by two mile constants of 25 and 400 fs The results tire compared to tert-butyl (t-C4H9), another tertiary radical investigated before. Time-dependent DFT calculations confirm the earlier suggestion that curve crossings along the C-C coordinate play all Important role in the excited-state deactivation