Complexes formed in collisions between ultracold alkali-metal diatomic molecules and atoms

We explore the properties of 3-atom complexes of alkali-metal diatomic molecules with alkali-metal atoms, which may be formed in ultracold collisions. We estimate the densities of vibrational states at the energy of atom-diatom collisions, and find values ranging from 3.9 to 350 K$^{-1}$. However, this density does not account for electronic near-degeneracy or electron and nuclear spins. We consider the fine and hyperfine structure expected for such complexes. The Fermi contact interaction between electron and nuclear spins can cause spin exchange between atomic and molecular spins. It can drive inelastic collisions, with resonances of three distinct types, each with a characteristic width and peak height in the inelastic rate coefficient. Some of these resonances are broad enough to overlap and produce a background loss rate that is approximately proportional to the number of outgoing inelastic channels. Spin exchange can increase the density of states from which laser-induced loss may occur.

Li Plating on Carbon Electrode Surface Probed by Low-Field Dynamic Nuclear Polarization 7Li NMR

Lithium deposition on graphite electrode not only reduces fast-charging capability of lithium ion batteries but also causes safety trouble. Here, a low-field 7Li dynamic nuclear polarization (DNP) is used to probe Li plating on the surfaces of three types of carbon electrodes: hard carbon, soft carbon and graphite. Owing to the strong Fermi contact interaction between 7Li and conduction electrons, the 7Li nuclear-magnetic-resonance (NMR) signal of Li metal deposited on electrode surface could be selectively enhanced by DNP. It is suggested that low-field 7Li DNP spectroscopy is a sensitive tool for investigating Li deposition on electrodes during charging/discharging processes.

Determining electron–nucleus distances and Fermi contact couplings from ENDOR spectra

The hyperfine coupling between an electron spin and a nuclear spin depends on the Fermi contact coupling aiso and, through dipolar coupling, the distance r between the electron and the...

Profiling astrophysically relevant MgC4H chains. An attempt to aid astronomical observations

ABSTRACT In this paper, we report results of an extensive theoretical study on MgC4H chains conducted at DFT and CCSD(T) levels motivated by the recent discovery of this species in IRC+10216. A detailed characterization of both neutral and charged species is presented, which include structural, chemical bonding and vibrational properties, rotational, centrifugal distortion and Watson l-type doubling constants, dipole moments, Fermi contact, and spin-rotation constants. In addition, we present ab initio estimates needed for subsequent astrochemical evolution modelling (e.g. dissociation energies, acidity, electron attachment, and ionization energies and related chemical reactivity indices). Possible formation pathways are also discussed. They comprise exchange, (radiative) association, dissociative recombination, and ion neutralization reactions. As an important result aiming at stimulating further observational searching, we suggest that MgC4H− anions should also be observable via rovibrational spectroscopy. The reason is twofold: (i) Neutral MgC4H0 chains possess a sufficiently large dipole moment consistent with dipole-bound anion states and large electron attachment cross-sections. (ii) MgC4H− anions possess a dipole substantially larger than MgC4H0 neutrals (and also larger than that estimated earlier for the longest astronomically detected C8H− anion). This makes MgC4H− anion intensities in rovibrational spectrum experimentally accessible even in the unlikely case of a relative abundance MgC4H−/MgC4H0 comparable to that of CH4, whose anion has the lowest relative abundance observed so far in space because weakly polar C4H0 chains do not support dipole-bound anion states. A suggestion on why, counterintuitively, the MgC2H abundance found in IRC+10216 was lower than that of the longer MgC4H is also presented.

Electrically tuned hyperfine spectrum in neutral Tb(ii)(CpiPr5)2 single-molecule magnet

A strong Fermi contact (FC)-driven and electrically tunable hyperfine interaction is predicted for the neutral Tb(ii)(CpiPr5)2 single-molecule magnet.

The Effects of Split Valence Basis Sets on Muon Hyperfine Interaction in Guanine Nucleobase and Nucleotide Structures

The DFT cluster method was employed to investigate the electronic structures and muonium hyperfine interactions in guanine nucleobase and nucleotide using three different basis sets. The total energy and Fermi contact values were calculated for muon trapped at carbon '8'. The three basis sets, 6-31G, 6-311G and 6-311G(d,p), were used in tandem with the B3LYP functional. There are significant quantitative differences in the calculated total energy. 6-311G(d,p) produced the lowest total energy as compared to the other basis sets. The lowering of the total energy is due to the increase in the number of basis functions to describe the atomic orbitals, which is consistent with the postulate on basis set completeness. The 6-31G basis set produced the muon Fermi contact value that is the closest to the experimental value. The calculated Fermi contact values for the nucleobase and nucleotide are significantly lowered in going from the double-zeta to the triple-zeta basis set by 5% and 4% respectively. The lowering of the Fermi contact value can be attributed to the extension of the triple-zeta basis set in describing the valence atomic orbitals. The presence of the sugar phosphate group in the nucleotide instead of the methyl group tends to lower the Fermi contact value. Thus, the sugar phosphate group should be taken into consideration when designing a calculation model.