This week I will start a little series of posts on matter-wave optics, beginning with a phenomenological review of what distinguishes a wave from a particle. Over time we will discuss a number of concepts that are fundamental to the regime of quantum mechanics but rather unintuitive in our everyday lives. Let’s see where it takes us.
This week starts with waves.
When you introduce a substituent to an aromatic system in organic chemistry you are mostly interested in the effect on the aromatic. The reason for this is that substituents are often attached in specific positions to steer the outcome of a following reaction.
In this study we examined the interplay between indole and a methoxy substituent. Depending on its position at the ring system, the methoxy group alters the energetic position of the excited states of indole by about 2500 cm-1. Interestingly, there is also a position-dependent influence of indole on the substituent. We observe that the relative energies of the conformers and their barriers for interconversion depend strongly on where the methoxy group is located at the chromophore. With this we can explain why for 4- and 5-methoxyindole only one conformation is observed in jet-experiments, while both conformers are present for 6-methoxyindole. More information can be found here.
In these lecture notes we review recent developments in far-field diffraction at a single nanomechanical grating and Kapitza-Dirac Talbot-Lau interferometry. Among others, it covers the following points:
- What is the influence of the van der Waals attraction on the matter-wave and how can we reduce it?
- Why are mechanical gratings not the optimal choice for biomolecules?
- What happens when a large molecule absorbs a photon in a standing light wave?
- How can absolute absorption cross sections of large molecules be measured in a matter-wave interferometer?
Additionally, we discuss our efforts to produce slow beams of intact biomolecules – a veritable challenge as a lot of biomolecules such as amino acids or peptides decompose when they get too hot.
The lectures notes will be published in press in “Les Houches Summer School, Session CVII–Current Trends in Atomic Physics, July 2016”, but you can find an electronic version also on the arXiv.
The first publication published in 2017 is a study about the photophysical identity of the lowest excited singlet states for three different fluoroindoles. We could show that the orientation of the transition dipole moment for substituted indoles is not a reasonable identifier for the nature of the excited state – La or Lb – in general, although the assignment is often based on this data. More information about these two states and why they are important can be found here.