One of the key questions underlying adenine's photochemistry following 266 nm excitation is whether or not the dissociative (1)pi sigma* state plays an active role in the ensuing dynamics. This work describes how laser fluence studies on the Ad(+) and H+ following photo-excitation using a combination of ns and fs UY pulses with time-of-flight mass-spectrometry, provides new evidence that implicates the contentious participation of the (1)pi sigma* state in the photochemistry of adenine. (C) 2007 Elsevier B.V. All rights reserved.