Lennard-Jones interaction parameters of Mo and W in He and N 2 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 ( DT 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 Mo 6 O 19 2- and W 6 O 19 2- had a DT CCS He value of 103 ± 2 Å 2 , and both Keggin ions PMo 12 O 40 3- and PW 12 O 40 3- had a DT CCS He value of 170 ± 2 Å 2 . Similarly, ion mobility experiments in N 2 led to DT CCS N2 values of 223 ± 2 Å 2 and 339 ± 4 Å 2 for Lindqvist and Keggin anions, respectively. Using optimized structures and partial charges determined from density functional theory calculations, followed by CCS calculations via the trajectory method, we determined Lennard-Jones 6-12 potential parameters ε , σ 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 2 , respectively. These parameters reproduced the CCS of polyoxometalates within 2% accuracy.