Ullrich Susanne, Schultz Thomas, Zgierski Marek Z, Stolow Albert
Steacie Institute for Molecular Sciences, National Research Council of Canada, Ottawa, Ontario, Canada K1A 0R6.
J Am Chem Soc. 2004 Mar 3;126(8):2262-3. doi: 10.1021/ja030532q.
We present femtosecond time-resolved photoelectron spectra of adenine in a molecular beam, recorded at pump wavelengths of 250, 267, and 277 nm. This leads to initial excitation of the bright S2(pipi*). Close to the band origin (277 nm), the lifetime is several picoseconds. Higher vibronic levels (267 and 250 nm excitation) show much shorter lifetimes of t < 50 fs, and we observe strong coupling between S2(pipi*) and S1(npi*). Rapid internal conversion (t < 50 fs) populates the lower lying S1(npi*) state which has a lifetime of 750 fs. At 267 nm, we found evidence for an additional channel which is consistent with the dissociative S3(pisigma*) state, previously proposed as an ultrafast relaxation pathway from S2(pipi*).
我们展示了在分子束中腺嘌呤的飞秒时间分辨光电子能谱，该能谱是在250、267和277 nm的泵浦波长下记录的。这导致了明亮的S2（ππ*）的初始激发。接近能带起源（277 nm）时，寿命为几皮秒。较高的振动态（267和250 nm激发）显示出短得多的寿命τ<50 fs，并且我们观察到S2（ππ*）和S1（nπ*）之间有强耦合。快速内转换（τ<50 fs）使较低的S1（nπ*）态布居，其寿命为750 fs。在267 nm处，我们发现了另一个通道的证据，该通道与先前提出的作为从S2（ππ*）的超快弛豫途径的离解S3（πσ*）态一致。
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