title: Inelastic x-ray scattering of dense solid oxygen: evidence for intermolecular bonding.
abstract: The detailing of the intermolecular interactions in dense solid oxygen is essential for an understanding of the rich polymorphism and remarkable properties of this element at high pressure. Synchrotron inelastic x-ray scattering measurements of oxygen K-edge excitations to 38 GPa reveal changes in electronic structure and bonding on compression of the molecular solid. The measurements show that O(2) molecules interact predominantly through the half-filled 1pi(g)* orbital <10 GPa. Enhanced intermolecular interactions develop because of increasing overlap of the 1pi(g)* orbital in the low-pressure phases, leading to electron delocalization and ultimately intermolecular bonding between O(2) molecules at the transition to the epsilon-phase. The epsilon-phase, which consists of (O(2))(4) clusters, displays the bonding characteristics of a closed-shell system. Increasing interactions between (O(2))(4) clusters develop upon compression of the epsilon-phase, and provide a potential mechanism for intercluster bonding in still higher-pressure phases.
authors.affiliation: High-Pressure Collaborative Access Team, Carnegie Institution of Washington, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439, USA.
authors.forename: Yue
authors.initials: Y
authors.lastname: Meng
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Eng
authors.forename: John S
authors.initials: JS
authors.lastname: Tse
authors.forename: Dawn M
authors.initials: DM
authors.lastname: Shaw
authors.forename: Michael Y
authors.initials: MY
authors.lastname: Hu
authors.forename: Jinfu
authors.initials: J
authors.lastname: Shu
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Gramsch
authors.forename: Chi-chang
authors.initials: CC
authors.lastname: Kao
authors.forename: Chichang
authors.initials: C
authors.lastname: Kao
authors.forename: Russell J
authors.initials: RJ
authors.lastname: Hemley
authors.forename: Ho-Kwang
authors.initials: HK
authors.lastname: Mao