Green fluorescent protein (GFP), the most widely used fluorescent protein for in vivo monitoring of biological processes, is known to undergo photooxidation reactions. However, the most fundamental property underpinning photooxidation, the electron detachment energy, has only been measured for the deprotonated GFP chromophore in the gas phase. Here, we use multiphoton ultraviolet photoelectron spectroscopy in a liquid-microjet and high-level quantum chemistry calculations to determine the electron detachment energy of the GFP chromophore in aqueous solution. The aqueous environment is found to raise the detachment energy by around 4 eV compared to the gas phase, similar to calculations of the chromophore in its native protein environment. In most cases, electron detachment is found to occur resonantly through electronically excited states of the chromophore, highlighting their importance in photo-induced electron transfer processes in the condensed phase. Our results suggest that the photooxidation properties of the GFP chromophore in an aqueous environment will be similar to those in the protein.

The complexes of the Ba atom and Ba+ cation with the rare gas atoms Ar, Kr, and Xe in the states associated with the 6s → 5d, 6p excitations are investigated by means of the multireference configuration interaction techniques. Scalar relativistic potentials are obtained by the complete basis limit extrapolation through the sequence of aug-cc-pwCVnZ basis sets with the cardinal numbers n = Q, T, 5, combined with the suitable effective core potentials and benchmarked against the coupled cluster with singles, doubles, and non-iterative triples calculations and the literature data available for selected electronic states. Spin-orbit coupling is taken into account by means of the state-interacting multireference configuration interaction calculations performed for the Breit-Pauli spin-orbit Hamiltonian. The results show weak spin-orbit coupling between the states belonging to distinct atomic multiplets. General trends in the interaction strength and long-range anisotropy along the rare gas series are discussed. Vibronic spectra of the Ba and Ba+ complexes in the vicinity of the 1S → 1P° and 2S → 2P° atomic transitions and diffusion cross sections of the Ba(1S0, 3DJ) atom in high-temperature rare gases are calculated. Comparison with available experimental data shows that multireference calculations tend to underestimate the interaction strength for excited complexes.

The low-lying electronic states of Yb isolated in a solid Ar matrix grown at 4.2 K are characterized through absorption and emission spectroscopy. Yb atoms are found to occupy three distinct thermally stable trapping sites labeled "red," "blue," and "violet" according to the relative positions of the absorption features they produce. Classical simulations of the site structure and relative stability broadly reproduced the experimentally observed matrix-induced frequency shifts and thus identified the red, blue, and violet sites as due to respective single substitutional (ss), tetravacancy (Tv), and hexavacancy (Hv) occupation. Prolonged excitation of the (1)S → (1)P transition was found to transfer the Yb population from hv sites into Tv and ss sites. The process showed reversibility in that annealing to 24 K predominantly transferred the Tv population back into Hv sites. Population kinetics were used to deduce the effective rate parameters for the site transformation processes. Experimental observations indicate that the blue and violet sites lie close in energy, whereas the red one is much less stable. Classical simulations identify the blue site as the most stable one.

Structures and energies of the trapping sites of manganese atom and dimer in solid Ar, Kr, and Xe are investigated within the classical model, which balances local distortion and long-range crystal order of the host and provides a means to estimate the relative site stabilities. The model is implemented with the additive pairwise potential field based on the ab initio and best empirical interatomic potential functions. In agreement with experiment, Mn single substitution (SS) and tetrahedral vacancy (TV) occupation are identified as stable for Ar and Kr, whereas the SS site is only found for Xe. Stable trapping sites of the weakly bound Mn dimer are shown to be the mergers of SS and/or TV atomic sites. For Ar, (SS + SS) and (TV + TV) sites are close in energy, whereas (SS + TV) site lies higher. The (SS + SS) accommodation is identified as the only stable site in Kr and Xe at low energies. The results are compared with the resonance Raman, electron spin resonance, and absorption spectroscopy data. Reproducing the numbers of stable sites, the calculations tend to underestimate the matrix effect on the dimer vibrational frequency and spin-spin coupling constant. Nonetheless, the level of agreement is found to be informative for tentative assignments of the complex features seen in Mn matrix isolation spectroscopy.

The electronic transitions of ytterbium atoms in a solid Xe matrix grown at 4.8 K are investigated. Absorption bands are detected in the regions of the gas-phase 6s2 1S0 → 4f135d6s2 and 6s2 1S0 → 6s6p 1P1 transitions. Both bands indicate that Yb atoms occupy multiple trapping sites, of which three are identified. Emission induced by the 6s2 1S0 → 6s6p 1P1 excitation is found to be concentrated entirely in the region of the 6s6p 3PJ → 6s2 1S0 decay, whereas the singlet emission is completely quenched. Multiple emission peaks are observed and the effects of annealing and prolonged irradiation on their amplitudes are found to be significant and are interpreted as a consequence of Yb population transfer from one type of site to another. Modeling of the ground-state site structure and stability predicts three Yb/Xe occupation types, substitutional (ss), tetravacancy (tv) and hexavacancy (hv), in order of decreasing stability. Their tentative associations with observed absorption and emission features are discussed. Time correlated single photon spectroscopy is used to determine the lifetimes of the individual emission bands. They are found to be different from each other with indications of a mixture of short- and long- lived 6s6p 3PJ fine-structure components and demonstrate distinct temperature dependencies. A dramatic decrease in the lifetime of the emission peak tentatively assigned to the most stable site with temperature is explained by a competition between the radiative and non-radiative decay paths of the 6s6p 3P1 state. The mechanism of the latter can be attributed to electron–phonon coupling as confirmed by a model of the temperature-dependence of the lifetime.