Intramolecular vibrational dynamics of the asymmetric =CH2 hydride stretchof isobutene

The eigenstate-resolved, high-resolution (5 MHz) infrared spectrum of the a symmetric =CH2 hydride stretch of isobutene has been measured using an elec tric resonance optothermal spectrometer (EROS). This vibrational band near 3087 cm(-1) was rotationally assigned with ground state microwave-infrared double-resonance spectroscopy. IVR rates from rotationally homogeneous IVR multiplets at values of total angular momentum, J ranging from J = 0 to J = 3 and K-a values of K-a = 0 to K-a = 2, were obtained. The average IVR lif etime for this vibrational mode is 105 ps and independent of rotational sta te. The experimental state density of the rotationless 0(00) vibrational st ate, approximately 150 states/cm(-1), is in good agreement with the direct count result of 99 states/cm(-1) using the C-3v(+) circle times C-3v(-) (G( 36)) molecular symmetry group. The lineshape profiles of the IVR multiplets are investigated in order to elucidate information concerning the dependen ce of IVR rates on the symmetry of the torsional wavefunction. We find that there is a common IVR rate among the various torsional symmetries. IVR lif etimes observed in the present study are compared to other asymmetric ethyl enic hydride stretch IVR rates measured in our laboratory. (C) 1999 Academi c Press.