The cis and trans structures of the NO dimer cation

The NO dimer cation, (NO)2+, has been studied using high-level ab initio calculations. The ground state is determined to be the trans isomer, which has C2h symmetry. The cis, C2v, isomer lies ca. 100 cm−1 above this, as calculated at the RCCSD(T)/aug-cc-pVQZ(no g)//UQCISD/6-311+G(3df) level of theory. The equilibrium geometry of the trans isomer has an N–N bond length of 2.25 Å and a NNO bond angle of 112°. A reassignment of the ZEKE spectrum of the NO dimer is postulated on the basis of calculated harmonic vibrational frequencies.