A. Lesarri et al., Rotational spectrum, ring-puckering vibration and ab initio calculations on 1,1-difluorocyclobutane, J CHEM PHYS, 111(14), 1999, pp. 6375-6384
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 couplin
g parameters, and the energy spacings Delta E-01 and Delta E-23. The spectr
um for the v(p)=4 to v(p)=6 ring-puckering states was satisfactorily accoun
ted 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 splitting
s Delta E-01 and Delta E-23. The calculated variation of the quartic centri
fugal distortion constants with the ring-puckering quantum number reproduce
s satisfactorily the experimental trends, confirming the validity of the de
rived potential function. Ab initio calculations with HF, MP2, and B3LYP de
nsity functional hybrid methods have been carried out for this molecule usi
ng different basis sets. The experimental and ab initio potential functions
, coupling terms, and ring-puckering dynamical parameters are compared. Fin
ally, an ab initio near-equilibrium structure is presented. (C) 1999 Americ
an Institute of Physics. [S0021-9606(99)31037-0].