OBSERVATION OF TUNNELING SPLITTINGS IN THE 10 MU-M INFRARED-SPECTRA OF CYCLOPROPYLAMINE AND PROPARGYLAMINE

Three vibrational bands for each of the primary amines, cyclopropylami ne and propargylamine, have been studied in the 900-1100 cm(-1) region using a 2 MHz resolution (fwhm) electric resonance optothermal molecu lar beam spectrometer with a microwave sideband CO2 laser. All the obs erved bands exhibit tunneling doublets with 3:1 relative intensities, indicative of amine proton interchange. No evidence for tunneling spli ttings has been observed in the ground-state microwave spectra of thes e molecules, although such splittings have been observed in the microw ave spectra of other primary amines. For trans-cyclopropylamine the v( 10) and v(23) fundamental bands and the v(13) + v(27) torsional combin ation band have been observed near 1020, 1045, and 1006 cm(-1), respec tively. The J = 0 tunneling splittings for v(10) and v(23) are 3.6(4) and 21.3(4) MHz. These splittings are essentially independent of J and K-a. For v(13) + v(27) the tunneling splittings vary from 923(14) MHz for K-a = 0 to 675(14) MHz for K-a = 4. Because the tunneling gaps in the ground state are unknown, these splittings measure only the diffe rence in tunneling splitting between the ground and excited states. Th e rotational progressions for the tunneling sublevels of v(10) and v(2 3) are well characterized by an asymmetric-top Hamiltonian, except for a Coriolis perturbation of the 928 level of ylo The rotational levels for the combination vibration are poorly characterized by an asymmetr ic rotor Hamiltonian. For transpropargylamine, the vs and v(9) fundame ntal bands and an unidentified combination band, presumably in Fermi r esonance with v(9), have been observed near 1076, 931, and 929 cm(-1) respectively. The J, K-a = 0 tunneling splittings, measuring the diffe rence in tunneling splitting between the ground and excited states, ar e +748(1) MHz for ys and -404(2) and -350(4) MHz for the Fermi diad, w ith the splittings for all three bands showing a strong K-a dependence . The origins of the tunneling splittings are discussed.