Insight into fundamental, overtone, and combination IR bands of surface and bulk Ba(NO3)2 by Ab Initio molecular dynamics

Vibrational characteristics of Ba(NO₃)₂, one of the key components in an important automotive catalytic technology, NOx storage and reduction (NSR), were investigated by ab initio molecular dynamics. In particular, the fundamental, overtone, and combination bands of surface and bulk Ba(NO₃)₂ were calculated and compared with experimental infrared (IR) spectra measured by internal and diffuse reflection sampling configurations. Using the densities of characteristic internal vibrational modes, the origins of the experimental IR bands in the regions of fundamental as well as overtone and combination vibrations were clarified. Furthermore, the molecular dynamics based vibrational analysis showed that the bands in the overtone and combination band region (1600-3000 cm^-1), typically neglected in NSR studies, contain chemically rich information and can assist in the firm identification of surface nitrates and their adsorption configurations.