Observation of the molecular response to light upon photoexcitation

• Published in: Nature communications Vol. 11; no. 1; p. 2157
• Main Authors: Yong, Haiwang, Zotev, Nikola, Ruddock, Jennifer M., Stankus, Brian, Simmermacher, Mats, Carrascosa, Andrés Moreno, Du, Wenpeng, Goff, Nathan, Chang, Yu, Bellshaw, Darren, Liang, Mengning, Carbajo, Sergio, Koglin, Jason E., Robinson, Joseph S., Boutet, Sébastien, Minitti, Michael P., Kirrander, Adam, Weber, Peter M.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01-05-2020; Nature Publishing Group; Nature Portfolio
• Subjects: 119/118; 639/638/440/94; 639/638/440/949; 639/638/563/758; 639/766/930/2735; 639/766/94; ATOMIC AND MOLECULAR PHYSICS; Chemical physics; Coherent light; Electromagnetic fields; Electron density; Electron states; Electrons; Energy absorption; excited states; Humanities and Social Sciences; imaging techniques; Light effects; Light sources; multidisciplinary; Photoabsorption; Photochemicals; Photoexcitation; Photosynthesis; quantum chemistry; Science; Science (multidisciplinary); Spatial discrimination; Spatial resolution; Ultraviolet radiation; X-ray scattering
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-020-15680-4

When a molecule interacts with light, its electrons can absorb energy from the electromagnetic field by rapidly rearranging their positions. This constitutes the first step of photochemical and photophysical processes that include primary events in human vision and photosynthesis. Here, we report the direct measurement of the initial redistribution of electron density when the molecule 1,3-cyclohexadiene (CHD) is optically excited. Our experiments exploit the intense, ultrashort hard x-ray pulses of the Linac Coherent Light Source (LCLS) to map the change in electron density using ultrafast x-ray scattering. The nature of the excited electronic state is identified with excellent spatial resolution and in good agreement with theoretical predictions. The excited state electron density distributions are thus amenable to direct experimental observation.
Photoabsorption is a fundamental process that leads to changes in the electron density in matter. Here, the authors show a direct measurement of the distribution of electron density when a cyclohexadine molecule is excited by pulsed UV radiation and probed by a time delayed X-ray pulse generated at LCLS.