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A microwave spectroscope and the microwave spectra of CHF[2]C1 and CHFC1[2] Mann, Cedric Robert

Abstract

A microwave spectroscope is described which operates in the region 23,000 to 27,000 mc./sec. Measurement of the frequencies of rotational absorption lines is achieved by comparison of the frequency of the signal from the source oscillator with the frequency of one of a set of standard microwave signals generated with auxiliary apparatus. The frequency of each of the standard signals is known to be better than 1 part in 10⁶ and the frequency of a rotational absorption line can be measured to .05 mc./sec. The spectroscope has been used to study the pure rotational spectra of the asymmetric top molecules CHF₂Cl and CHFCl₂. Thirty-two absorption lines have been observed for CHFCI₂ and the frequencies measured. Twenty absorption lines have been observed and the frequencies measured for CHF₂CI. All the lines in CHF₂Cl are doublets, the separation of the two lines in each doublet varying from .59 mc./sec. to 6.18 mc./sec. A graphical method of analyzing the spectrum of CHF₂CI is developed and applied. The relative intensities of different types of transitions are calculated. It is shown that the strongest absorption lines observed should be due to transitions where ∆ J = 0,∆Շ= +1 and that the values of J for the energy states between which these transitions occur should be greater than 12. The hyperfine structure due to the quadrupole moment of the chlorine nucleus is calculated and it is shown that, for J greater than 12, the hyperfine structure cannot be completely resolved. In this case, each line should appear as a doublet. A method of using the hyperfine structure to help analyze the spectrum is given. By this means, the four lines centered around 26,441 mc./sec. are identified as being the completely resolved hyperfine structure of the transition 10₃₇ - 10₄₇. The frequency of the absorption lines due- to the two transitions 11₅₈ - 11₄₈ and 9₃₆ - 9₄₆ are predicted to be approximately 20,500 mc./sec. and 31,50.0 mc./sec, and it is shown that if these lines are observed the moments of inertia of the molecule can be calculated.

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