Abstract
The equilibrium geometries, binding energies and vibrational spectra of CH3F, CH2F2 and CHF3, nitrous acid and their C-F center dot center dot center dot center dot HONO-bonded complex have been investigated with the standard 6-31G** basis set ab initio calculation performed at the Moller-Plesset second-order (MP2) level. In all these complexes, a strong C-F center dot center dot center dot center dot HONO, halogen-hydrogen bond is formed. The strength of the hydrogen-bonded complexes show a decreasing trend as one go from CH3F to CHF3 with both cis- and trans-form of nitrous acid. Large hydrogen-bond distances are predicted in cis-HONO complex with flouromethanes as compare to trans-HONO complex. Furthermore, C-F bond decrease in HONO (trans) complexes has been observed, whereas in HONO (cis) complex C-F bond increase is observed. This is an unusual observation. The red shift in all the complexes of nitrous acid with flouromethanes correlated well with C-F bond lengthening.