Physical Chemistry Seminar: Professor Javier Aoiz, Universidad complutense de Madrid

Physical Chemistry Seminar: Professor Javier Aoiz, Universidad complutense de Madrid, Sapp Center Lecture Hall, 4:30pm (Host: Richard Zare)

About the Speaker:

F. Javier Aoiz is Full Professor at the Department of Physical Chemistry I of the University Complutense of Madrid. He was born in 1954, and received his M.Sc. degree in Chemistry (Physical Chemistry) from the Madrid University Complutense (UCM) in 1976, and the Ph. D. degree in Chemistry from the same University in 1981. He was a Fulbright postdoctoral fellow at the Department of Chemistry of Columbia University (New York, USA) for a period of two years (1981-1982), under the supervision of late Professor Richard B. Bernstein. He has been visiting professor at the University of Nottingham (1989, 1993), University of California Los Angeles (USA) (1990) and at Oxford University (1995, 2005-2006). He became permanent faculty member of the Department of Physical Chemistry University Complutense of Madrid as Associated Professor (1984-1999) and appointed for a Full Professor chair in 2000. Javier Aoiz is member of the Spanish Royal Society of Chemistry, American Physical Society and for a period of four years, member of the Editorial board of the Physical Chemistry and Chemical Physics journal and currently member of the Ownership board of that journal. 

He was awarded with the 2006 Prize of the Spanish Royal Society of Chemistry for his research in Physical Chemistry. He is the leader of the group of Reaction Dynamics and Femtochemistry at the UCM and he has been director of the UCM Multiphoton Spectroscopy and Femtochemistry facility until 2015. He has been member of scientific and organization committees of international conferences and summer schools, referee of national and international research projects through Spanish Agencies (ANEP, MEC) and the U.K. Royal Society and referee of international journals (JCP, JPC,CPL, PCCP, Nat. Chem.) in the field of Physical Chemistry/Chemical Physics and specifically in theoretical reactive and inelastic collision dynamics.

Javier Aoiz is author of about 250 reviewed papers (6700 citations; h-index 46) in and theoretical and experimental Physical Chemistry (Reaction Dynamics, Spectroscopy) and more than 60 invited lectures and talks at international conferences. His research interest is centred in theoretical studies of reactive and inelastic collisions, stereodynamics, and experimental work on photodissociation dynamics with lasers and imaging techniques, molecular beam studies of reactive collisions, laser multiphoton ionisation (REMPI) spectroscopy, time-of-fight mass spectrometry, etc. 

About the Seminar: 

"Young double-slit experiments in chemical reactions: Quantum interferences in reactive scattering."

The Young's double-slit experiment applied to interferences of single electrons has been considered one of the most beautiful and intriguing experiment in physics [1–3] and has become a standard example in quantum mechanics (QM) textbooks for illustrating wave-particle duality. In the experiment, electrons, one at a time, are shot against a screen that contains two small openings (slits). The detection of the transmitted electrons results in an interference pattern, similar to that observed when light waves instead of electrons are used. Moreover, the experiment has also been carried out using heavier particles,[4–6] such as fullerene molecules, leading to similar conclusions and demonstrating the quantum nature of these large and presumably more classical molecules. It might be wondered whether such interference effects occur in chemical reactions and, if so, how they affect the reaction observables.

Interferences in scattering processes are genuine quantum phenomena that appear whenever two seemingly distinct classical trajectories lead to the same outcome. They are common in elastic and inelastic scattering but are seldom observable in chemical reactions since it requires fully initial and final state selection and sufficiently narrow collision energy distributions. Very recently [7,8], it has been shown that, for certain states, interferences produce a characteristic oscillation pattern that governs the angular distributions for the H + D2  exchange reaction [7,8]. In this talk, we will discuss the interpretation of recent experimental results for the H+D2 reaction obtained using the photoloc technique [7-9] here in Stanford. It was found that the angular distributions for certain states display characteristic oscillation pattern in the backward region.  The comparison between quasiclassical trajectory (QCT) and QM calculations evinces that the oscillation pattern arises when groups of partial waves than span different ranges of the total angular momentum give rise to scattering at the same deflection angles. Interestingly, the various groups of partial waves can be assigned to different classical mechanisms that take place under certain conditions. Moreover, the analysis of the quantum interferences serves to identify those mechanisms. The phenomenon is analogous to that found in the double (and multiple)-slit experiment wherein the analysis of the diffraction pattern allows us to determine the double-slit characteristics more precisely than what would have happened if the behavior were purely classical.

We will show that the conditions under which interferences determine the shape of the angular distribution depend on the shape of the potential energy surface, the collision energy [9], and the initial and final states.  In particular, it will be also shown how interferences depend on the initial rotational state j of the D2(v =0, j) reagent and diminish in strength with increasing rotation [8]. We will present a detailed explanation for this behavior and how each dynamical scattering mechanism has a dependence on the helicity, W, the projection of the initial rotational angular momentum j of the D2 reagent on the approach direction.  Each helicity corresponds to a different internuclear axis distribution, with the consequence that the dependence on W reveals the preference of the different quasiclassical mechanisms as a function of approach direction.

[1] R. P. Feynman, R. B. Leighton and M. Sands, Lectures on Physics, Vol 3, Chp. 3. Addison-Wesley 1964.

[2] Jim Baggot, The Quantum Story: A history in 40 moments. Oxford University Press. 2015.

[3] S. Hawking and L. Mlodinov, The Grand Design Random House Inc. 2011.

[4] M. Arndt, O. Nairz, J. Vos-Andreae, C. Keller, G. van der Zouw and A. Zeilinger, Nature 401, 680-682 (1999)

[5] O. Nairz, M. Arndt and A. Zeilinger, Am. J. Phys. 71, 319-325 (2003).

[6] S. Gerlich, S. Eibenberger, M. Tomandl, S. Nimmrichter, K. Hornberger, P. J. Fagan, J. Tuxen, M. Mayor and M. Arndt, Nat. Commun., 2011, 2, 263.

[7] P. G. Jambrina, D. Herráez-Aguilar, F. J. Aoiz, M. Sneha, J. Jankunas  and R. N. Zare, Nat. Chem. 7, 661-665 (2015)

[8] P. G. Jambrina, J. Aldegunde, F. J. Aoiz, M. Sneha, and R. N. Zare. Chem. Sci. 7, 642-649 (2016).

[9] Mahima Sneha, Hong Gao, Richard N. Zare, P. G. Jambrina, M. Menéndez, and F. J. Aoiz.

J. Chem. Phys. 145, 024308 (2016)