A COUPLED-CLUSTER STUDY OF XON (X=H, F, CL), AND THE XON[--]XNO TRANSITION-STATES

The XON molecules (X=H, F, and Cl) have been studied using the CCSD(T) method. Equilibrium geometries, dipole moments, harmonic frequencies and infrared intensities are predicted. The X-O bond distance is shown to be abnormally long for X=F and Cl, which is attributed to the degree of ionic bonding and the stability of NO+. Stability of the XON molecule relative to the XNO isomer is shown to increase in the order HON < FON < ClON, although even ClON is 27.7 +/- 0.9 kcal/mol (0 K) less stable than ClNO. The XON reversible XNO transition states are also investigated. FON and ClON possess the lowest barrier heights, but these are sufficiently large that isomerization should not be rapid at low temperatures.