Accurate equilibrium structures for small polyatomic molecules, radicals and carbenes

Abstract

The paper reports on recent efforts to establish accurate equilibrium structures for small polyatomic molecules, radicals and carbenes most of which are of relevance to interstellar cloud chemistry, combustion processes or atmospheric chemistry. Among these are the well-known interstellar cyanopolyynes HC(3)N and HC(5)N, members of the series NC(2n)N, HC(2n+1)P and NC(2n)P, linear silicon carbides of type SiC(2n) and pure carbon chains up to C(14), the radicals HC(3)O, HOCO and CH(2)CHO as well as cumulene carbenes of type H(2)C(n). Whenever possible, a mixed experimental/theoretical procedure is employed which makes use of accurate experimental values for the ground-state rotational constants of a sufficiently large number of different isotopomers plus the results of coupled cluster calculations ( variant CCSD(T)). In less favourable cases, the transfer of well-established correction parameters as developed from related smaller molecules appears to be the method of choice.