The photodetachment process of cyclopentoxide (cyc-C5H9O-) has been studied using a direct ab initio molecular dynamics method with the HCTH/6-31G(d) DFT theory. The ring-opening reaction of photodetached product cyclopentoxy (cyc-C5H9O) to the 5-oxo-pentan-1-yl radical is mainly addressed. The lifetime of cyclopentoxy is predicted to be 3.05 +/- 0.07 ps. The photoelectron kinetic energy spectrum of cyc-C5H9O- is approximately simulated by using a simple reflection approach and a post passive scheme for including the nuclear dynamics effects, which is made to compare with experimental results. (C) 2007 Elsevier B.V. All rights reserved.