Lennard-Jones interaction parameters of Mo and W in He and N from collision cross-sections of Lindqvist and Keggin polyoxometalate anions.

Drift tube ion mobility spectrometry (DTIMS) coupled with mass spectrometry was used to determine the collision cross-sections (CCS) of polyoxometalate anions in helium and nitrogen. As the geometry of the ion, more than its mass, determines the collision cross-section with a given drift gas molecule, we found that both Lindqvist ions MoO and WO had a CCS value of 103 ± 2 Å, and both Keggin ions PMoO and PWO had a CCS value of 170 ± 2 Å. Similarly, ion mobility experiments in N led to CCS values of 223 ± 2 Å and 339 ± 4 Å for Lindqvist and Keggin anions, respectively. Using optimized structures and partial charges determined from density functional theory calculations, followed by CCS calculations the trajectory method, we determined Lennard-Jones 6-12 potential parameters , of 5.60 meV, 3.50 Å and 3.75 meV, 4.40 Å for both Mo and W atoms interacting with He and N, respectively. These parameters reproduced the CCS of polyoxometalates within 2% accuracy.