Fermi resonances in the rotational structure of the infrared spectra of methyl iodide

High-Resolution Infrared Spectra of ν5 and ν3 + ν6 of CH3I

“…For the I V3= 1, V6= 1) state we find Vo= 1410.31, a A = -S.3SX 10-2 , D K = 1.21X 10-3 cm-t, and s= 0.203. Our value of S55 is in agreement with that found by Morino et al3 although the value they used for Ao is somewhat smaller than the one we used. The value of S for the I V3= 1, V6= 1) state should be close to S66 which we have determined by analysis of the V6 band l6 to be S66= 0.210.…”

“…Ihe I Va= 1, V6= 1) where the Fermi operator, H", was assumed to be simply the cubic normal-coordinate force constant kZ56 multiplying the cubic product of the vibrational coordinates qaq5q6 and to be diagonal in the quantum numbers f, K, and t. We took as a starting set of band constants the values which Morino et al 3 had obtained for the unperturbed vibrational energies of Jl5 and Jl3+V6, the rotational constants of the excited state and the Fermi-resonance parameter Wand the values obtained by Orville-Thomas, Cox, and Gordy8 for the groundstate rotational constants B", D/' and DJK". Since the ground-state constants were obtained from microwave measurements we chose to constrain them in the leastsquares refinement of the band parameters.…”

“…From the nature of these frequency displacements and the selection rules it now seems clear to us that there is an x-y Coriolis interaction between the states I V5= 1) and I V3= 1, V6= 1) in addition to the Fermi resonance between these states established by Morino, Nakamura, and Yamamoto. 3 The Q branch assigned to RQ(l, 2)+ consists of two components at 1469.4 and 1470.4 cm-I as illustrated in Fig. 1 (b) and we find, in addition to the series of lines already assigned to the R R( 1,2)+ branch and associated with the Q-branch component at 1469.4 cm-I , a second series of R-branch lines assignable to the other Q branch at 1470.4 cm-I which we assign to the other component of the R R( 1,2)+ branch and attribute the splitting of these branches to the Coriolis resonance.…”

13C frequency shifts and the general harmonic force fields of methyl chloride, bromide and iodide

“…We have also been able to use new Dj and DjK centrifugal distortion data for CDzC1, CD3Br, and CDaI [11], and improved frequency and Coriolis data from several recent independent investigations of all these CH3X and CDsX molecules [12][13][14][15][16][17][18].…”

“…]-Recalculated from the data of [13] by us, using A"= 5-158 cm -1 [18]. $ Recalculated from the data of [13,16] by Maki and Hexter [18]. w Values of shifts, and hence band centres of vl and 2v5, derived directly by Q branch matching.…”