• T S Jaseja

Articles written in Proceedings – Section A

• The ionic character of singly bonded molecules

The overlap factors for bond electrons in various diatomic halides are calculated making use of a simple relation where the overlap factor is an inverse exponential function of the difference between the two atomic radii of the molecule concerned. These overlap factors together with the hybridization values of 15 percent for Cl, and 10 percent for Br and I are used to calculate the ionic characters for various diatomic molecules from the values of the nuclear quadrupole coupling constants obtained by earlier workers. These ionic characters are then plotted against electronegativity differences and the points are found to be fairly well represented by a smooth curve. It is shown that this curve can in general be used for the determination of the ionic characters in the halogen containing single bonds of certain polyatomic molecules. The quadrupole coupling constants are calculated from the ionic characters obtained from the curve and are compared with those observed. The effects of the distortion of the closed shells and of the neighbouring ions oneQq are discussed.

• The microwave spectrum of methyl cyanide andl-type doubling in CH3CN, CH3NC, CH3CCH and CF3CCH

The microwave spectrum of Methyl cyanide molecule has been obtained corresponding to the transitions J=0→1, J=1→2 and J=2→3 in the ground vibrational state as well as in the excited degenerate vibrational statesv8=1 andv8=2. The frequencies of the lines are measured by using a secondary standard spectrograph taking mostly the ammonia lines as standards. The value of the vibration-rotation interaction constanta8 has been found to be −27·3±0·4 mc./sec. The spectrum obtained for the transitions J=1→2 and J=2→3 withv8=1 has been understood on the basis of Nielsen’s theory ofl-type doubling in symmetric top molecules. The assignments give a value of 0·94 for the coriolis interaction constant which is consistent with the value obtained from the infra-red spectral data.

The earlier work on similar transitions involvingl-type doubling in the molecules CH3NC, CH3CCH and CF3CCH has been reviewed and the inconsistencies in the values of some parameters like coriolis interaction constant ζ and the rotation constant DJK obtained by earlier workers from their assignments are pointed out. A reassignment of the transitions and the involved parameters removes these inconsistencies and yields coriolis interaction constants which are in close agreement with those obtained from infra-red spectral data. The following are the different ζ values obtained: $$\begin{gathered}\zeta _8 in CH_3 NC = 0 \cdot 93 \hfill \\\zeta _{10} in CH_3 CCH = 1 \cdot 00 \hfill \\\zeta _9 in CH_3 CCH = 0 \cdot 95 \hfill \\\zeta _{10} in CF_3 CCH = 0 \cdot 6 \hfill \\\end{gathered}$$

•