Far-UV photochemical bond cleavage of n -amyl nitrite: Bypassing a repulsive surface

We have investigated the deep-UV photoinduced, homolytic bond cleavage of amyl nitrite to form NO and pentoxy radicals. One-color multiphoton ionization with ultrashort laser pulses through the S₂ state resonance gives rise to photoelectron spectra that reflect ionization from the S₁ state. Time-resolved pump-probe photoionization measurements show that upon excitation at 207 nm, the generation of NO in the v = 2 state is delayed, with a rise time of 283 (16) fs. The time-resolved mass spectrum shows the NO to be expelled with a kinetic energy of 1.0 eV, which is consistent with dissociation on the S₁ state potential energy surface. Combined, these observations show that the first step of the dissociation reaction involves an internal conversion from the S₂ to the S₁ state, which is followed by the ejection of the NO radical on the predissociative S₁ state potential energy surface.