Atoms and small molecules interacting with strong external fields.

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The fundamental-physics part of the proposal aims for a more accurate determination of a fundamental constant and of properties of the proton, which most of the matter in the universe is made of. The fine-structure constant determines the strength of the coupling between charged particles, and also to photons, i.e., to light. It is known to nine digits to date, and has been determined by a number of methods in solid-state physics and in atomic spectroscopy. It needs to be known better for tests of the theory of electron-photon interactions, called quantum electrodynamics. While this is the most precisely known part of the standard model, there is a continuing push for more precise knowledge due to progress in atomic spectroscopy. The proton charge radius puzzle is of extreme importance in this context. Atomic hydrogen spectroscopy has hit a roadblock five years ago, since measurements on an artificial form of hydrogen (made in the laboratory), where the electron is replaced by a muon, has yielded a different radius value (0.84 femtometer), as opposed to 0.88 fm, as determined by a combination of regular hydrogen spectroscopic measurements. The muonic hydrogen determination is much more precise, since the heavier muon, as compared to the electron, is much closer to the proton on average, and therefore more sensitive. The large radius value of 0.88 fm had become the accepted value by the CODATA world group that is the caretaker of fundamental constants, since the most precise electron-proton scattering experiments of 2010 (from Mainz, Germany) also supported this value.We have re-analyzed the Mainz data on e-p scattering, and found that they were not inconsistent with the small proton radius. Our re-analysis of the Mainz data relies on support from particle theory provided by a group in Spain. We also propose to also resolve a controversy between the magnetic charge radius value that currently exists between the Mainz and Jefferson Lab (USA) determinations. In related work we are modelling some of the regular hydrogen spectroscopy experiments (both past and a current one under way at York) to understand why the past one favoured a large charge radius value.In the more applied area we are proposing to continue recent work on the water molecule, which is important in the context of radiation therapy. We will extend current work on strong-electric field ionization of H2O to intense laser field ionization with the aim to understand the properties of water under extreme conditions. This work extends our state-of-the-art work on collision-induced ionization and fragmentation which agrees well with experimental results.