Complexes of lithium cation with nitrogen trifluoride:: a computational investigation on the structure and stability of Li+-(NF3) isomers

The structure and stability of the still experimentally unknown Li+-(NF3) ions have been theoretically investigated at the B3LYP, QCISD, QCISD(T), and CCSD(T) levels of theory in conjunction with the 6-311G(d), 6-311+G(2d), and 6-311+G(3df) basis sets. Irrespective of the employed theoretical level, it was found that the ligation of Li to the F atoms of NF3 may occur in two distinct ways, leading to the formation of the monocoordinated isomer 2 and the dicoordinated isomer 3. These two isomeric ions are practically degenerate and more stable than the nitrogen-coordinated isomer 1 by ca. 6 kcal mol(-1). In addition, the optimized geometries of the Li+-(NF3) isomers 1, 2, and 3 and the analysis of their chemical bonding indicate the formation of ion-dipole complexes between Li+ and NF3. The Li+ ion affinity of NF3 at 298.15 K is computed as 15.6 kcal mol(-1) at the B3LYP/6-311+G(3df) level of theory, 13.3 kcal mol(-1) at the QCISD(T)/6-311+G(2d) level of theory, and 12.8 kcal mol(-1) at the CCSD(T)/6-311+G(2d) level of theory. These values are large enough to suggest the possibility that lithiated NF3 could be actually observed as a stable species in the gas phase. From the applied point of view, this finding supports the proposal that Li+ ion attachment mass spectrometry, recently proposed by Fujii [J. Phys. Chem. A 104 (2000) 9613] as a conceivable technique to quantify the emissions of the greenhouse gases CF4, C2F6, C4F8, and SF6, from the electronic industry, could be also employed to quantify the emissions of NF3, one of the perfluorocompounds most extensively used in semiconductor technology. (C) 2001 Elsevier Science B.V. All rights reserved.