A method of measurement of absolute wavelengths of absorption bands in the infrarad is described. A Fabry-Perot etalon with bare glass plates is interposed in series with the absorption tube which superimposes the Edser Butler type fringes on the absorption spectrum. The methods used for calibration of the etalon are described. The precision of frequency measurement is of the order of ±0.02 cm−1 in the region of 1.7μ.
The absorption bands of CH3Br in the region 5800 to 6200 cm−1 were measured by this method. Two parallel and three perpendicular bands are reported. The P, Q, and R structure of the parallel component of the 2ν4 band was well resolved enabling the determination of ν0 = 6046.42, B′ = 0.31875, and A′ = 5.027 cm−1. The separation of the P and R maxima of the 2ν1 is 23 cm−1. The band origins of the perpendicular components 2ν4(6095.61 cm−1), ν4 + ν1(5940.4 cm−1), and ν4 + 2ν5(5878.1 cm−1) were determined on the basis of intensity and alternation of intensity due to nuclear spin of the H atoms. ζ for the perpendicular component of 2ν4 was determined as −0.128.
© 1953 Optical Society of AmericaFull Article | PDF Article
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