15min:

LOU DEGLIUMBERTO, DAVID S. PERRY, University of Akron, Akron, OH 44325; WENDY HEISERMAN, REBECCA COOK, HOWARD D. METTEE, Youngstown State University, Youngstown, OH 44555; ROBERT L. SAMS, Pacific Northwest National Laboratory, Richland, WA 99352; GEORG O. SORENSEN, University of Copenhagen, DK-2100, Copenhagen, Denmark.

In the high resolution spectrum of nitromethane near 1584 cm^-1 each of the zeroth order transitions of the lowest internal rotor state is split into a clump of 4 or 5 rovibrational transitions. Individual perturbing (dark) states are followed as a function of the J ' , K_a ' , and K_c ' rotational quantum numbers. Four stages of vibration-torsion-rotation coupling are identified: (i) sub-picosecond c -axis Coriolis coupling to a torsionally excited state dark vibration ( ₇ + ₁₀ or ₅), (ii) a -axis Coriolis coupling between A₁ ' and A₂ ' torsional states of the dark vibration, (iii) c -axis Coriolis coupling of the dark vibration back to dark rotational states of the asymmetric N-O stretch, and (iv) at J ' =8 and higher a strong coupling to a second torsionally excited dark vibration .