Stimulated Raman spectroscopy has been used to study rotationally resolved Q-branch of the v(3) band. This spectrum is analyzed with data from the v(9) fundamental, v(9) + v(4) - v(4) hot band and transitions from v(4) and 3v(4) torsional bands. One torsional component of the v(3) fundamental is near degenerate with its interacting partner v(4) = 5 of the ground state torsional bath. The coupling was modeled using a Fermi-type interaction. The introduction of the Fermi-type interaction causes a large change in the barrier height for the ground vibrational state and makes the barrier shape parameter redundant, indicating the vibrational contributions to the experimental barrier shape are dominant. (c) 2006 Elsevier B.V. All rights reserved.