Structures and electron affinities of the di‐arsenic fluorides As 2 F n /As 2 F ( n = 1–8)

Developments in the preparation of new materials for microelectronics are focusing new attention on molecular systems incorporating several arsenic atoms. A systematic investigation of the As 2 F n /As 2 F systems was carried out using Density Functional Theory methods and a DZP++ quality basis set. Global and low‐lying local geometric minima and relative energies are discussed and compared. The three types of neutral‐anion separations reported in this work are: the adiabatic electron affinity ( EA ad ), the vertical electron affinity ( EA vert ), and the vertical detachment energy ( VDE ). Harmonic vibrational frequencies pertaining to the global minimum for each compound are reported. From the first four studied species (As 2 F n , n = 1–4), all neutral molecules and their anions are shown to be stable with respect to AsAs bond breaking. The neutral As 2 F molecule and its anion are predicted to have C s symmetry. We find the trans FAsAsF isomer of C 2h symmetry and a pyramidalized vinylidene‐like AsAsF isomer of C s symmetry to be the global minima for the As 2 F 2 and As 2 F species, respectively. The lowest lying minima of As 2 F 3 and As 2 F are vinyl radical‐like structures FAsAsF 2 of C s symmetry. The neutral As 2 F 4 global minimum is a trans ‐bent (like Si 2 H 4 ) F 2 AsAsF 2 isomer of C 2 symmetry, while its anion is predicted to have an unusual fluorine‐bridged (C 1 ) structure. The global minima of the neutral As 2 F n species, n = 5–8, are weakly bound complexes, held together by dipole–dipole interactions. All such structures have the AsF m AsF n form, where (m,n) is (2,3) for As 2 F 5 , (3,3) for As 2 F 6 , (4,3) for As 2 F 7 , and (5,3) for As 2 F 8 . For As 2 F 8 the beautiful pentavalent F 4 AsAsF 4 structure (analogous to the stable AsF 5 molecule) lies about 30 kcal/mol above the AsF 3 · · · AsF 5 complex. The stability of AsF 5 depends crucially on the strong AsF bonds, and replacing one of these with an AsAs bond (in F 4 AsAsF 4 ) has a very negative impact on the molecule's stability. The anions As 2 F , n = 5–8, are shown to be stable with respect to the AsAs bond breaking, and we predict that all of them have fluorine‐bridged or fluorine‐linked structures. The zero‐point vibrational energy corrected adiabatic electron affinities are predicted to be 2.28 eV (As 2 F), 1.95 eV (As 2 F 2 ), 2.39 eV (As 2 F 3 ), 1.71 eV (As 2 F 4 ), 2.72 eV (As 2 F 5 ), 1.79 eV (As 2 F 6 ), 5.26 eV (As 2 F 7 ), and 3.40 eV (As 2 F 8