All calculations have been performed at the DFT level of theory using the B3LYP hybrid functional.68–70 This functional has already been shown to give good results for the calculation of higher-order properties in earlier work.46,71 Dunning's correlation-consistent polarized triple-ζ (cc-pVTZ) basis set72 has been used. The study was conducted for methanimine (CH2NH), and nitromethane (CH3NO2) and its mono- (CH2DNO2) and di-deuterated (CHD2NO2) isotopomers. Two conformations (eclipsed and staggered) have been considered for the non-deuterated isotopomer and four (H-eclipsed, D-eclipsed, H-staggered and D-staggered) for each deuterated isotopomer (cf. Fig. 1).