Rotational spectrum, ring-puckering vibration and ab initio calculations on 1,1-difluorocyclobutane

摘要

The rotational spectra of the ground and first five ring-puckering excited states of 1,1-difluorocyclobutane have been investigated in the centimeter-(8-40 GHz) and millimeter-wave regions (96-106 and 144-159 GHz). Analysis of the spectra for the pairs of coupled vibrational states v_p = 0/1 and v_p = 2/3 has been carried out using two-state Hamiltonians, yielding accurate rotational and centrifugal distortion constants, vibration-rotation coupling parameters, and the energy spacings #DELTA#E_(01) and #DELTA#E_(23). The spectrum for the v_p = 4 to v_p = 6 ring-puckering states was satisfactorily accounted for in terms of effective semi-rigid Hamiltonians for each vibrational state. A double minimum ring-puckering potential function with a barrier to ring inversion of 231(4) cm~(-1) has been obtained from the analysis of the vibrational dependence of the rotational constants and inversion splittings #DELTA#E_(01) and #DELTA#E_(23). The calculated variation of the quartic centrifugal distortion constants with the ring-puckering quantum number reproduces satisfactorily the experimental trends, confirming the validity of the derived potential function. Ab initio calculations with HF, MP2, and B3LYP density functional hybrid methods have been carried out for this molecule using different basis sets. The experimental and ab initio potential functions, coupling terms, and ring-puckering dynamical parameters are compared. Finally, an ab initio near-equilibrium structure is presented.