[MOS] Tomorrow 3/3 - Modern Optics and Spectroscopy Seminar with Marcos Dantus

[Christine Brooks]

There will be a Modern Optics and Spectroscopy Seminar held tomorrow, Tuesday, March 3rd in NE47-189<http://whereis.mit.edu/?go=NE47> at 12pm (please note location)

Marcos Dantus
Michigan State University

“Extreme chemical reactivity in solution and in the gas phase”

Acid-base equilibria drive most chemical reactions and are paramount for sustaining life processes. Stronger acids or bases are associated with a greater driving force, related to the greater Gibbs free energy of reaction. Unfortunately, the use of very strong acids or bases is limited because they are not compatible with the medium where the reaction takes place. For example, concentrated sulfuric acid reacts violently with most solvents, and sodium can explode if dropped in water. Fortunately, extreme acidity or basicity can be achieved by harnessing the energy of photons. A change of electronic configuration can bring about orders of magnitude greater acidity or basicity. This last statement will be illustrated by the characterization of a super photobase. This compound (FR0-SB), with pKa of 7 in the ground state has a pKa* of 21 in the excited state [Angew. Chem. Int. Ed. 57, 14742 (2018)]. Changes in the proton affinity of FR0-SB will be discussed following one- and two-photon excitation.  Even more extreme reactivity can be achieved in the gas phase via strong laser field ionization. For example, alcohols under strong laser fields undergo exotic chemical processes involving making and breaking of multiple chemical bonds that result in the formation of H3+, H2O+, and H3O+.The formation of H3+, following strong-field photodissociation of methanol, is preceded by the formation of a neutral H2 molecule that roams the parent ion and extract a proton [Sci. Rep. 7, 4703 (2017)] as illustrated in [Figure 1]. Site-specific details and femtosecond time-resolved dynamics of H3+ formation for a series of alcohols have been obtained through a combination of time-resolved mass spectrometry, photoion-photoion coincidence measurements, and ab initio calculations [Nat. Commun. 9, 5186 (2018)]. The yield of these and related strong-field reactions has been recently found to be sensitive to the spectral phase of femtosecond laser pulses [J. Chem. Phys. 150, 044303 (2019)]. The existence of organic molecules and water in the universe is due in great part to the existence of H3+, because, as a Brønsted–Lowry acid, H3+ donates protons to carbon and oxygen atoms as well as to more complex organic molecules. Our findings provide mechanistic and dynamic information about the chemistry of H3+.

Refreshments served immediately following the seminar!

Christine Brooks
Administrative Assistant
Massachusetts Institute of Technology
Department of Chemistry
77 Massachusetts Ave, 6-333
Cambridge, MA 02139
p: 617.253.7239
e: cbrooks at mit.edu<mailto:cbrooks at mit.edu>

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