Internal motion in weakly bound halomethane complexes

Abstract

A complementary blend of computational and spectroscopic methods has been
used to analyze three halomethane complexes which exhibit different types of internal
motion. In CH2FrCO2, the CH2F2 undergoes a "rocking" motion which inverts the dipole
moment component along the c axis. For thjs complex, the spectra of six isotopologues
were measured and an experimental structure was determined (see figure). The barrier to
inversion was 142(3) cm·1 based on an experimental AE (AE is the energy difference
between v=0+ and v=ff), which is in good agreement with the ab imtio ZPE-corrected
barrier of 122 cm •1
. Upon comparison with similar complexes, a trend was established
where the magrutudes of dipole/quadrupole moments and barrier for internal motion are
indirectly proportional. The other two complexes, CHBrFrH 2O and CHCIF2-H2O,
revealed an internal rotation of the water molecule. The spectra of two isotopologues
(79Br and 81Br) of CHBrFrH 2O were assigned, and an approximate structure was
determjned (see figure). A barrier to internal rotation for each complex was determined
using a AE value of 16008(416) MHz: 115(14) cm·1 for CHBrF2-H2O and 105(10) cm·1
for CHClF2-H2O, which are consistent with the ab initio predictions for each species.
Analysis of a series ofhalomethane-water complexes revealed that the dipole moment of
the halomethane, the halogen-hydrogen distance, and barrier energy are indirectly
proportional.

Date of Award	2012
Original language	American English
Awarding Institution	Eastern Illinois University
Supervisor	Sean A. Peebles (Supervisor)