Thu, 23.05.2019  |  14:00 PM
IKZ, R316/317
MBI Colloquium

Nuclear-driven Electronic Coherences in Molecules

Dr. Albert Stolow | University of Ottawa, Canada

talks about

Electronic coherences in molecules has emerged as a ‘grand challenge’ in molecular sciences due to the role that electronic correlations and dynamics play in structure and bonding. In the field of attosecond science, electronic coherences can be prepared by attosecond pulses, producing purely electronic wavepackets which persist while the atoms are ‘frozen’ (i.e. a few femtoseconds). Once the atoms unavoidably start to move, the wavepacket could dephase and the electronic coherence would be lost. However, some suggested that nuclear motion could modify or even induce electronic coherences.

 

Prior theoretical investigations of nuclear-driven electronic coherences by Mukamel, Santra, Levine and others were all based on Molecular Frame (MF) calculations. These made use of coherent X-ray techniques. We make a very simple but important point. For gas phase molecules, the full Hamiltonian necessarily includes the rotational degrees of freedom. These exist only in the Lab Frame (LF), not in the MF. This leads to significant new insights and opportunities, as well as dramatic technical simplifications, for the probing of ultrafast electronic coherences in gas phase molecules. Here we present our study of electronic coherences in a polyatomic molecule (NH3) driven by nuclear dynamics.

 

Any MF electronic coherences (whether produced by attosecond pulses, electronic-nuclear coupling, or both) initiated by polarized laser pulses will necessarily create a net anisotropy of the electronic probability distribution in the LF. As a LF anisotropy, it can be directly measured in the LF by any ultrafast angle-resolved scattering technique which is sensitive to electron probability distributions, such as X-ray or electron scattering, or as shown here: photoemission.