Radical cations of trans-stilbene (1), trans-4-methoxystilbene (2), and 2,4-(3), 3,4-(4), 3,5-(5), and 4,4 ' -dimethoxystilbene (6) were generated from the resonant two-photon ionization (RTPI) in acetonitrile using a excimer laser (308 nm, 25 ns). The photostationary state of the S 1 and S n is attained within the laser flash duration of 25 ns in the RTPI of 1-6. Based on the photostationary state analysis, the relationship of Φ i o n ≃I 2 was obtained for the RTPI of 1-4 with shorter singlet lifetimes (<100 ps), while Φ i o n ≃I was obtained for the RTPI of 5 and 6 with longer singlet lifetimes (>300 ps).