TY - JOUR
T1 - Ultrafast Nonadiabatic Cascade and Subsequent Photofragmentation of Extreme Ultraviolet Excited Caffeine Molecule
AU - Marciniak, Alexandre
AU - Yamazaki, Kaoru
AU - Maeda, Satoshi
AU - Reduzzi, Maurizio
AU - Despré, Victor
AU - Hervé, Marius
AU - Meziane, Mehdi
AU - Niehaus, Thomas A.
AU - Loriot, Vincent
AU - Kuleff, Alexander I.
AU - Schindler, Baptiste
AU - Compagnon, Isabelle
AU - Sansone, Guiseppe
AU - Lépine, Franck
N1 - Funding Information:
In this article, we have pushed these experiments one step further by investigating the dynamics of XUV-excited caffeine molecules, which is relevant for both astrochemistry and biophysics. Indeed, caffeine consists of a purine backbone (see Figure S2) which is also the basis for many other prebiotic building blocks such as adenine, guanine, or xanthine that have been detected in carbonaceous meteorites18 suggesting that they have been synthesized in the early age of the solar system, where they are processed by XUV radiation. Besides, caffeine molecules have been investigated in UV transient absorption spectroscopy in liquid phase by Chen and Kohler19 demonstrating the existence of a 500 fs nonradiative decay mechanism which may involve CI accessed via out-of-plane deformations of caffeine. In our study, we performed XUV pump−IR probe measurements in neutral caffeine produced in gas phase. We resolved the dynamics induced by the XUV excitation on the femtosecond time scale allowing to extract ultrafast relaxation dynamics of a few tens of fs through specific fragmentation channels of the caffeine cation. This time scale is understood in terms of an internal conversion (IC) cascade through a large density of states that is probed by IR photoexcitation of the unstable dications that dissociate. This interpretation is supported by quantum chemistry calculations.
Publisher Copyright:
© 2018 American Chemical Society.
PY - 2018/12/20
Y1 - 2018/12/20
N2 - Ultrafast XUV chemistry is offering new opportunities to decipher the complex dynamics taking place in highly excited molecular states and thus better understand fundamental natural phenomena as molecule formation in interstellar media. We used ultrashort XUV light pulses to perform XUV pump-IR probe experiments in caffeine as a model of prebiotic molecule. We observed a 40 fs decay of excited cationic states. Guided by quantum calculations, this time scale is interpreted in terms of a nonadiabatic cascade through a large number of highly correlated states. This shows that the correlation driven nonadiabatic relaxation seems to be a general process for highly excited states, which might impact our understanding of molecular processing in interstellar media.
AB - Ultrafast XUV chemistry is offering new opportunities to decipher the complex dynamics taking place in highly excited molecular states and thus better understand fundamental natural phenomena as molecule formation in interstellar media. We used ultrashort XUV light pulses to perform XUV pump-IR probe experiments in caffeine as a model of prebiotic molecule. We observed a 40 fs decay of excited cationic states. Guided by quantum calculations, this time scale is interpreted in terms of a nonadiabatic cascade through a large number of highly correlated states. This shows that the correlation driven nonadiabatic relaxation seems to be a general process for highly excited states, which might impact our understanding of molecular processing in interstellar media.
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U2 - 10.1021/acs.jpclett.8b02964
DO - 10.1021/acs.jpclett.8b02964
M3 - Article
C2 - 30444124
AN - SCOPUS:85058904275
VL - 9
SP - 6927
EP - 6933
JO - Journal of Physical Chemistry Letters
JF - Journal of Physical Chemistry Letters
SN - 1948-7185
IS - 24
ER -