13C frequency shifts and the general harmonic force fields of methyl chloride, bromide and iodide
TL;DR: In this paper, general harmonic and hybrid orbital force fields have been calculated for methyl chloride, bromide and iodide using the best available frequency, Coriolis coefficient, and centrifugal distortion data, including the recent 13C frequencies for the chloride and ionide.
Abstract: General harmonic and hybrid orbital force fields have been calculated for methyl chloride, bromide and iodide using the best available frequency, Coriolis coefficient, and centrifugal distortion data, including the recent 13C frequencies for the chloride and iodide. Anharmonicity corrections were made to the fundamental frequencies using Dennison's rule and x values of 0·04 for CH stretching, 0·02 for CH bending, and 0·01 for CX stretching modes. These were the most reasonable values which did not seriously over-compensate for the product rule deficiencies in the 12C and 13C frequencies. The 13C and CD3X frequency information was input in the form of frequency shifts from the 12CH3X frequencies. All 12 parameters in the most general harmonic force fields are determined with significance for the first time, although the previously uncertain parameters F12 and F13 are only determined with good precision when the 13C frequency data are utilized in addition to the other information. The signs of F12, F45 and ...
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TL;DR: In this paper, the atomic polar tensors of the methyl halide molecules (CH3X) were determined using infrared intensity data reported by Russell, Needham, and Overend.
Abstract: Atomic polar tensors have been determined for H, C, and X atoms of the methyl halide molecules (CH3X), using infrared intensity data reported by Russell, Needham, and Overend. The signs for the ∂p/∂Qi’s have been chosen by considering Coriolis coupling constants, agreement between intensity parameter values for CH3X and CD3X, and by considering the values of the atomic polar tensors calculated by CNDO methods for CH3F and CH3Cl. The resulting atomic polar tensors show systematic trends for the CH3X molecules as X change from F to I. The possibility that atomic polar tensors can be transferred from one molecule to another (with some allowance for expected trends) cannot be ignored. Atomic effective charges for each atom have been calculated, and ξH is found to be nearly constant for the four molecules. Additional properties of the atomic polar tensor are examined, including the anisotropy. A ''modified bond moment hypothesis'' appears to be reasonably successful in modeling the infrared intensities of the methyl halides.
160 citations
TL;DR: In this paper, Ellis R, Lippincott, and Kirklin present a posthumous account of the National Bureau of Standards' first classifications of the metric system, and present address of Duane R, Kirklin.
139 citations
TL;DR: An extensive critique of studies on methyl bromide and all its isotopic varieties with special stress on their rotational, vibrational, and rovibrational spectra was given in this paper.
112 citations
TL;DR: In this paper, an analysis of the v 3, 2v 3, and v 1 parallel bands and the v 4 and v 6 perpendicular fundamentals have been made for 13CH3F in terms of the rotational structure observed with a resolution of ∼ 0·2 cm-1.
Abstract: Analyses of the v 3, 2v 3, and (predominantly) v 1 parallel bands, and of the v 4 and v 6 perpendicular fundamentals have been made for 13CH3F in terms of the rotational structure observed with a resolution of ∼0·2 cm-1. In addition, the band centres of the strongly Coriolis-interacting v 2 and v 5 fundamentals are accurately located. Some elucidation of the complex Fermi resonance interactions in the 3000 cm-1 region is achieved through study of spectra of crystalline samples. This enables all three components of the v 1, 2v 2, 2v 5 0 triad to be observed for both 12CH3F and 13CH3F, and estimates to be made for the unperturbed vibration frequencies. The 13C frequency shifts determined for all six fundamentals are used in conjunction with existing frequency, Coriolis ζ, and centrifugal distortion data for CH3F, CD3F, CHD2F and CH2DF, to determine the general harmonic force field for methyl fluoride. The extra shift data enable all 12 parameters of the force field to be fixed within narrow limits for the f...
106 citations
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TL;DR: In this paper, the best values of the twelve force constants in the most general harmonic potential field were obtained to fit twenty-two independently observed experimental data, these being the six vibration frequencies, three Coriolis zeta constants and two centrifugal stretching constants D J and D JK, for both CH 3 F and CD 3 F.
229 citations
TL;DR: In this paper, the authors used a general refinement program developed for use with an electronic computer to obtain the best set of force constants consistent with all available data on vibration frequencies, Coriolis zeta constants and centrifugal stretching constants for all possible isotopes.
185 citations
TL;DR: In this paper, absolute intensity measurements have been made on the fundamental vibrations of methyl chloride, bromide and iodide, and their fully deuterated derivatives, by integrating the optical density over the absorption bands.
Abstract: Absolute intensity measurements have been made on the fundamental vibrations of methyl chloride, bromide, and iodide, and their fully deuterated derivatives, by integrating the optical density over the absorption bands. The bands were fully pressure broadened by using up to 80 atmos of foreign gas. Band separations were made graphically. The results are analyzed in terms of the dipole moment derivatives with respect to symmetry coordinates in the molecule, (∂p/∂Si). The data on the different isotopic species are shown to yield consistent results, and this requirement of consistency has also been used as an aid in the analysis. In the E‐class vibrations the signs of the dipole moment derivatives have been determined unambiguously by assuming the permanent dipole to be directed CH3+–X—.
149 citations
TL;DR: In this paper, a method for imposing any desired constraint on the force field obtained in a force constant refinement calculation is discussed, and the results of unconstrained calculations, and of three different constrained calculations, are reported.
125 citations
TL;DR: In this paper, the potential energy functions found by Chang for the methyl halides have been put into valence-type form and revised to eliminate inconsistencies and to accord with the true nontetrahedral geometry and the normal frequencies (corrected for Fermi resonance and anharmonicity).
Abstract: The potential‐energy functions found by Chang for the methyl halides have been put into valence‐type form and revised to eliminate inconsistencies and to accord with the true (nontetrahedral) geometry and the normal frequencies (corrected for Fermi resonance and anharmonicity). The resulting valence‐type force constants and normal coordinates are given for light (CH3) and heavy (CD3) chlorides, bromides, and iodides.
122 citations