The singlet with a C 3 ring: the probable candidate of HC 6N and C 7H 2

Abstract

The geometrical structures of various stationary points in the HC 6N and C 7H 2 molecules were investigated using the second-order Møller-Plesset perturbation method with the Huzinaga-Dunning D95** basis set. The relative stability ladder to the most stable structure was determined using the SDCI + Q method with the general contraction scheme of the [4s2p1d/2s1p] atomic natural orbital basis set. Within 1 eV, eleven and eight stationary points were found for the HC 6N and C 7H 2 molecules, respectively. For each molecule the two singlets containing a C 3 ring are very stable. Only a linear structure was obtained for the triplet. Both the skelton structures and the energy relationships of the HC 6N and C 7H 2 molecules are similar to each other. The most stable singlets in both molecules lie about 7 kcal mol −1 below the corresponding linear triplets. The skeletons of the HC 6N and C 7H 2 molecules and the relative energy relationships of the isomers are similar to those of HC 4N and C 5H 2, where the most stable isomer is also a singlet containing a C 3 ring.