Internal Dynamics in Halogen-Bonded Adducts: A Rotational Study of Chlorotrifluoromethane-Formaldehyde

摘要

The rotational spectra of two isotopologues of the 1:1 complex between chlorotrifluoromethane and formaldehyde have been recorded and analyzed by using Fourier-transform microwave spectroscopy. Only one rotamer was detected, with the two constituent molecules held together through a Cl center dot center dot center dot O halogen bond (R-Cl center dot center dot center dot O= 3.048 angstrom). The dimer displays two simultaneous large-amplitude intramolecular motions. The internal rotation of formaldehyde around its symmetry axis (V-2 = 28(5) cm(-1)) splits all the rotational transitions into two component lines with a relative intensity ratio of 1:3. On the other hand, the almost free internal rotation (V-3 approximate to 2.5 cm(-1)) of the CF3 symmetric top increases the "rigid" value of the rotational constant A by almost one order of magnitude. In addition, all the transitions display a hyperfine structure due to the Cl-35 (or Cl-37) nucleus quadrupole effects.