MOLECULAR-STRUCTURES, RELATIVE STABILITIES AND ELECTRIC-DIPOLE MOMENTS OF HC7N, C7NH AND HC7-XNCX (X=1-6) - AN AB-INITIO INVESTIGATION

Ab initio MP2/4-31G* calculations are performed to determine the mole cular structures, relative stabilities and dipole moments of HC7N and its isomers C7NH and HC7-xNCx, with x = 1-6. HC7N is found to be the m ost stable structure, the other molecules being less stable by over 70 kcal mol(-1), except for HC6NC, which is less stable by 34.3 kcal mol (-1). All of the structures are strongly polar, with electric dipole m oments in the range 4-12 D. The dipole moments of the molecules HC7N, CnNH and HCn-1NC also increase as n increases. Rotational constants (B -0) are estimated using a scaling procedure based on MP2/4-31G* calcu lations performed on a group of similar molecules. The estimated B-0 v alue for HC7N is 564.5 MHz, in excellent agreement with the experiment al value of 564.00074 +/- 0.000016 MHz.