Study on the rovibrational interactions and a(1)/a(2) splittings in the nu(3)/nu(5)/nu(6) triad of CH3D

High-resolution Fourier transform infrared spectrum of CH3D has been record ed in the region of the fundamental bands upsilon(3), upsilon(5), and upsil on(6) between 900 and 1700 cm-l. High sensitivity of the equipment used as well as high accuracy of the recorded line positions gave the possibility o f assigning the first-time transitions with the upper state J quantum numbe r up to 23. In the analysis the new ground vibrational state information [O . N. Ulenikov, G. A. Onopenko, N. E. Tyabaeva, J. Schroderus, and S. Alanko , J. Mel. Spectrosc. 193, 249-259 (1999)] were used. In addition, modificat ion of the Hamiltonian model of the interacting vibrational states (upsilon (3) = 1), (upsilon(5) = 1), and (upsilon(6) = 1) allowed the theoretical de scription of numerous effects and peculiarities in the spectrum. In particu lar, sets of a,la, splittings have been assigned and explained, not only fo r upper state K = 1 and 2 but also for K = 4 and 5. Moreover, unusually gia nt exotic splittings have been found for K = 7. The spectroscopic parameter s reproducing the initial experimental energies with accuracy close to the experimental uncertainty have been determined. (C) 2000 Academic Press.