Friday, July 20, 2012

A Paramagnetic Bonding Mechanism for Diatomics in Strong Magnetic Fields

Kai K. Lange, E. I. Tellgren, M. R. Hoffmann and T. Helgaker Science 2012, 337, 327 (Paywall)

A new bonding mechanism
As chemists we are familiar with two types of strong bonds occurring between atoms, covalent and ionic. This paper shows that when very strong magnetic fields (of the order of 105 T) are applied, a third bonding mechanism arrises. Helgaker and co-workers term this perpendicular paramagnetic bonding.

Binding triplet H2
Whilst previous Hartree-Fock calculations have shown that the lowest triplet state of H2 becomes bound in strong magnetic fields, this investigation uses the recently developed LONDON code to demonstrate the same phenomena at the Full-CI level. Similar calculations (again, with a very strong magnetic field) on the triplet state of He2 show a considerable strengthening of the interaction between the constituent atoms.

The nature of this bonding
By examining the behaviour of the molecular orbitals under different orientations relative to the external magnetic field, the authors note a stabilisation of antibonding orbitals in the perpendicular orientation, leading to a new type of bonding interaction. Although the potential of a new chemical bonding mechanism is undoubtably exciting, the magnetic fields required are beyond those that can be currently generated in a lab. However, such fields are present on some stellar objects and the findings of this paper are likely to aid in the spectroscopy of such bodies.