Argon matrix Raman spectrum of LiO2. Bonding in the M+O2− molecules and the ionic model

Abstract

The Raman spectrum of LiO2 in argon matrices has been observed using 4880 Å excitation. The intraionic (O–O)− mode was observed as a sharp intense band at 1097 cm−1; the symmetric interionic (Li+–O2−) mode was recorded as a weaker broad feature at 694 cm−1. Oxygen-18 and lithium-6 substitution confirmed these vibrational assignments. The trend of increasing O2− vibrational frequency with increasing alkali atomic weight in the M+O2− molecules is rationalized using the Rittner ionic model of polarizable ion pairs.