Excited state non-adiabatic dynamics of pyrrole: a time-resolved photoelectron spectroscopy and quantum dynamics study.
Excited state non-adiabatic dynamics of pyrrole: a time-resolved photoelectron spectroscopy and quantum dynamics study.
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DOI：
10.1063/1.4907529
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发表时间：
2015-02
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通讯作者：
Guorong Wu;S. Neville;O. Schalk;T. Sekikawa;M. Ashfold;G. Worth;A. Stolow
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作者：
Guorong Wu;S. Neville;O. Schalk;T. Sekikawa;M. Ashfold;G. Worth;A. Stolow
利用时间分辨光电子能谱和波包传播相结合的方法研究了吡咯在242-217 nm波长范围内激发的动力学行为。激发接近吡咯的电子光谱的起源，在242和236 nm，被发现导致在一个单一的时间尺度上小于20 fs的电离窗口的系统的超快衰减。通过假设系统被激发到A2（πσ（π））态，与先前的实验和理论研究雅阁，充分解释了这种行为。在较短波长的激发之前被假设主要导致明亮的A1（ππ（π））和B2（ππ（π））态的布居。在这里，我们提出了时间分辨的光电子光谱在泵浦波长为217 nm的详细的量子动力学计算，连同最近的重新解释吡咯的电子光谱[S。P. Neville和G. A. Worth，J.Chem.Phys.140，034317（2014）]，表明当吡咯在其电子光谱的近UV部分中的能量下被激发时，B1（πσ（π））态（迄今被认为是光学暗的）的布居可以直接发生。B1（πσ（π））态在小于20 fs的时间尺度上通过N-H解离和内转换衰变到A2（πσ（π））态.
The dynamics of pyrrole excited at wavelengths in the range 242-217 nm are studied using a combination of time-resolved photoelectron spectroscopy and wavepacket propagations performed using the multi-configurational time-dependent Hartree method. Excitation close to the origin of pyrrole's electronic spectrum, at 242 and 236 nm, is found to result in an ultrafast decay of the system from the ionization window on a single timescale of less than 20 fs. This behaviour is explained fully by assuming the system to be excited to the A2(πσ(∗)) state, in accord with previous experimental and theoretical studies. Excitation at shorter wavelengths has previously been assumed to result predominantly in population of the bright A1(ππ(∗)) and B2(ππ(∗)) states. We here present time-resolved photoelectron spectra at a pump wavelength of 217 nm alongside detailed quantum dynamics calculations that, together with a recent reinterpretation of pyrrole's electronic spectrum [S. P. Neville and G. A. Worth, J. Chem. Phys. 140, 034317 (2014)], suggest that population of the B1(πσ(∗)) state (hitherto assumed to be optically dark) may occur directly when pyrrole is excited at energies in the near UV part of its electronic spectrum. The B1(πσ(∗)) state is found to decay on a timescale of less than 20 fs by both N-H dissociation and internal conversion to the A2(πσ(∗)) state.