Shinnosuke Saëki

Infrared band intensities of formaldehyde and formaldehyde‐d2

The infrared band intensities of formaldehyde and formaldehyde‐d2 have been measured in the gas phase using an FT–IR spectrometer. The effect of the polymerization of the sample molecule was minimized to measure the correct intensities. When the bands overlapped each other, their individual intensities have been determined by a band simulation calculation taking account of the Coriolis interactions. The signs of the dipole moment derivatives (∂p/∂Qi) have completely been determined by the least‐squares method, and the results were compared with those obtained by the molecular orbital calculation (CNDO/2) and by the analyses of the Coriolis interactions. The local intensity parameters of the CH2 group of this molecule were calculated and compared with the corresponding ones of ethylene.

Infrared absorption intensities of methane and fluoromethanes

Abstract The i.r. absorption intensities of methane and its deutero- and fluoro-derivatives; CH 4 , CD 4 , CH 3 D, CHD 3 , CH 2 D 2 , CF 4 , CH 3 F, CHF 3 , and CDF 3 , have been measured under high pressure. The intensity analysis has been carried out and the derivatives of molecular dipole moment with respect to a bond length or a valence angle have been determined as intensity parameters by the least squares method. The rotational correction required for the intensity consideration on a non-totally symmetric vibration of dipolar molecules is discussed briefly. For each molecular species the converged values of the parameters have been compared with the calculated ones by the CNDO/2 and INDO methods, and the most plausible solutions have been determined.

Calculation of infrared band intensities of various chlorinated methanes

Abstract Infrared band intensities of three molecular species CHCl 3 , CDCl 3 and CCl 4 , were measured in the vapour phase and the band intensity data of thirteen kinds of various chlorinated methanes, from methane to carbon tetrachloride, have been interpreted by means of as few as possible common intensity parameters. The parameters have been determined by using the least squares method from the observed data on the basis of the valence-optical theory. As a result, it has been proved that for almost all electro-optical parameters, it is possible to determine values which are commonly applicable to all chlorinated methane molecules, but for μ CH and ∂μ CH / ∂ r CH , it is not possible to find commonly applicable values.

Vibrational frequencies, infrared absorption intensities and energy differences between rotational isomers of propyl halides

Abstract Infrared absorption intensities of fundamental bands of propyl halides n -C 3 H 7 Cl, n -C 3 H 7 Br and n -C 3 H 7 I were measured in the pure liquid state. In order to obtain L matrix data necessary for the intensity computation, normal frequencies of the rotational isomers were calculated, and LSFF force constants were determined by the least squares method so as to attain the best fit between the observed and calculated frequencies. By applying the absolute intensity method, energy differences between the rotational isomers were evaluated, which are in quite good agreement with values obtained by the temperature variation method.

Calculation of infrared band intensities of methylene chloride in vapour and liquid phases

Abstract Infrared band intensities of three isotopic species of methylene chloride have been measured in the vapour phase and in dilute solution, and the results obtained for each phase have been interpreted on the basis of the valence-optical theory. The eleven intensity parameters determining the band intensities of these species have been obtained using the method of least squares from the observed intensities, and those parameters estimated for each phase have been compared in relation to the observed spectral changes.

Infrared intensities and Coriolis interactions in methylene fluoride

The individual intensities of the Coriolis interacting ν9, ν3, and ν7 bands of CH2F2 molecule were separately obtained through computer simulation technique. A similar analysis was carried out for the ν8 and ν2 diad, and ν9, ν3, and ν7 triad of CD2F2. The intensities of ν1 and ν6 bands of both CH2F2 and CD2F2 molecules were also reexamined. The obtained results were utilized to determine the sign of the dipole moment derivatives with respect to the normal coordinates. An evidence of a failure of the ’’CH stretching criterion’’ was found in the case of the antisymmetric CH stretching vibration of this molecule.

Infrared intensities of methyl fluoride: Determination of the signs of the dipole moment derivatives

Since the problem was presented by Abbate and Gussoni, resolution of the confusion on the infrared intensities of methyl fluoride has been hoped for. In the present study, the experimental data reported so far on this subject have been reinvestigated to find finally that the intensity value reported on the ν6 band of the CD3F molecule was very much in error and therefore caused essentially the present problem. By using the new data, an intensity analysis has been carried out again, and a unique set of solutions for the infrared intensity parameters has been determined for this molecule. The resulting parameter values are found to be in perfect accord with what chemical intuition predicts them to be.

Coriolis interactions and infrared intensities in fluoroform

Infrared intensities of the fundamental bands of the CHF3 molecule were remeasured. The Coriolis interaction between ν3 and ν5 bands as well as that between ν6 and ν5 bands was analyzed to determine the sign of the perturbation. As a result, the relative signs of all the (∂p/∂Qi)’s in this molecule have been determined without using the CNDO/2 method or an ab initio calculation. An empirical rule on the sign of the CF bond intensity parameters is proposed by the name of ’’CF‐bond criteria’’, according to which a negative dipole moment is enhanced in the direction of the displacements of the F atoms in both the CF stretching and CF deformation modes. Further, a possibility is suggested to extend this rule to all halogen atoms.

Determination of energy differences between rotational isomers of chloroacetyl chloride, bromoacetyl bromide and dichloroacetyl chloride by the absolute infrared intensity method

Abstract In order to determine the dihedral angle of the gauche isomer of CH 2 ClCOCl, normal frequencies and band intensities have been calculated at various assumed rotational angles of the gauche form. It has been shown by these calculations that the most probable value of the dihedral angle is about 105°. By applying the “absolute intensity method” and using the observed intensities of CH 2 C1COC1 and CH 2 BrCOBr measured in solution, the energy differences between, the rotational isomers of these molecules have been evaluated. The “direct intensity ratio method” has also been proposed as a simplified method to obtain the energy difference, and its applicability has been discussed. The energy differences of CH 2 ClCOCl, CH 2 BrCOBr and CHCl 2 COCl determined by these two methods have been compared with those determined previously by the temperature variation method.

A determination of the transition dipole moment of μa←s and μs←a of the ν2 band of NH3

Infrared absorption intensities of vibration-rotation lines of ν2 of NH3 were measured using a FT-IR spectrometer, and the values of the transition dipole moment of s ← a and a ← s transitions were determined. They were found to be μa←s = 0.236(4)D and μs←a = 0.248(7)D. μa←s is slightly greater than μa←s, the ratio μa←sμs←a being 0.960(5). This result was explained by taking into account the anharmonicities of both the potential energy and dipole moment functions.