Time-resolved photoelectron

Althorpe S C and Seideman T 1999 Molecular alignment from femtosecond time-resolved photoelectron angular distributions nonperturbative calculations on NO J. Chem. Phys. 110 147... 

Structure, then the time-resolved photoelectron spectra [20, 21] could reveal signatures of two different intermediate structures, representing two different pathways on the PES. Transient absorption spectroscopy and other femtosecond time-resolved techniques may also be applicable to this problem. 

In addition to the natural improvements expected in the accuracy of the measurements, and the increased scope in the types of systems examined, new techniques go beyond the issue of thermochemistry to allow for very detailed studies of reaction dynamics. The investigation by Zewail and co-workers of the reactivity of planar COT" on the femtosecond time scale is likely only the beginning. Time-resolved photoelectron spectroscopy, for example, has recently been used to map the potential energy surfaces for the dissociation of simple ions IBr and l2. " Although applications in the field of organic reactive molecules are likely far off, they are now possible. 

Hudock et al. [126] used the ab initio molecular dynamics multiple spawning method to go beyond the static picture based on PES and include the time dependent dynamical behavior and predict time-resolved photoelectron spectroscopy results. According to these results the first ultrafast component of the photoelectron spectra of uracil corresponds to relaxation on the S2 minimum rather than nonadiabatic transitions to the Si state. The authors suggest that the radiationless relaxation from... 

Ullrich S, Schultz T, Zgierski MZ, Stolow A (2004) Direct observation of electronic relaxation dynamics in adenine via time-resolved photoelectron spectroscopy. J Am Chem Soc 126 2262... 

Hudock HR, Levine BG, Thompson AL, Satzger H, Townsend D, Gador N, Ullrich S, Stolow A, Martinez TJ (2007) Ab initio molecular dynamics and time-resolved photoelectron spectroscopy of electronically excited uracil and thymine. J Phys Chem A 111 8500-8508... 

Most of the theoretical work regarding the utility of time-resolved photoelectron angular distributions to probe electronic, vibrational, and rotational dynamics have also concerned neutral photoionization.(Adapted from Sanov, 2002)... 

D. M. Neumark We are currently carrying out somewhat different femtosecond experiments in which time-resolved photoelectron spectroscopy is used to probe the photodissociation dynamics of negative ions. In these experiments, an anion is photodissociated with a femtosecond laser pulse. After a time delay, the dissociating anion is pho-todetached with a second femtosecond pulse and the resulting photoelectron spectrum is measured. The photoelectron spectrum as a function of delay time provides a detailed probe of the anion photodissociation dynamics. First results have recently been obtained for the photodissociation of I2. 

TIME-RESOLVED PHOTOELECTRON SPECTROSCOPY OF NONADIABATIC DYNAMICS IN POLYATOMIC MOLECULES... 

We turn now to a more detailed description of the photoionization probe step in order to clarify the ideas presented above. Time-resolved photoelectron spectroscopy probes the excited-state dynamics using a time-delayed probe laser pulse that brings about ionization of the excited-state wave packet, usually with a single photon... 

Figure 7. Time-resolved mass spectrometry. AU-trcms-(2, 4, 6, 8) decatetraene was excited to its 5 2 electronic origin with a femtosecond pulse at A-pump — 287 nm. The excited-state evolution was probed via single-photon ionization using a femtosecond pulse at ApIObe = 235 nm. The time resolution in these experiments was 290 fs (0.3 ps). The parent ion CioH signal rises with the pump laser, but then seems to stay almost constant with time. The modest decay observed can be fit with a single exponential time constant of 1 ps. Note that this result is in apparent disagreement with the same experiment performed at Xprobe — 352 nm, which yields a lifetime of 0.4 ps for the S2 state. The disagreement between these two results can be only reconciled by analyzing the time-resolved photoelectron spectrum.

Figure 8. Time-resolved photoelectron spectra revealing vibrational and electronic dynamics during internal conversion in DT. (a) Level scheme in DT for one-photon probe ionization. The pump laser prepares the optically bright state S2. Due to ultrafast internal conversion, this state converts to the lower lying state Si with 0.7 eV of vibrational energy. The expected ionization propensity rules are shown S2 —> Do + e (ei) and Si —> D + (b) Femtosecond time-...

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