Absolute Determination of Refractive Indices of Gases at 47.7 Gigahertz

Abstract

The refractive index of a gas is determined to high accuracy by measuring the change in the resonant frequency when the gas is admitted to a previously evacuated microwave cavity. This measurement was made at a frequency of 47.736 GHz, and is the first such measurement in this frequency range.The resonant frequency of the cavity is detected by means of a hybrid tee bridge circuit. When the cavity is matched to the waveguide the null at resonance is very sharp, and the frequency can be set to ±S parts in 10 8 • Two types of resonant structures were used in this measurement, a conventional cylindrical cavity and a Fabry-Perot resonator using one plane and one spherical mirror. Measurements were made with both structures on each of the gases, and the agreement between the two was within the limits of experimental error. Because the Fabry-Perot resonator has no side walls, air could be passed through it much more easily, and it is therefore preferred for use with moist air.The values of (n-1)X10 6 for the gases at O°C and 760 Torr are as follows: Dry C02 free air 288. 13±O.OS, Argon 277.48±O.OS, Carbon dioxide 49S.16±O.08, Helium 34.S1±O.OS, Hydrogen 13S.77±O.OS, Nitrogen 293.81±O.07, Oxygen 266.9S±O.OS.The primary values of these results lies in their increased accuracy over previous measurements and their confirmation of existing accurate data on these gases. In addition the use of the Fabry-Perot resonator as a refractometer is demonstrated and its advantages under certain conditions discussed.

Theoretical investigation of boundary contours of ground-state atoms in uniform electric fields

“…However, there are only 11 data whose measurement errors are less than 2.1% among the 17 experimental data. The 9 of the 11 accurate experimental data are in groups VIII and I, they are He [25], Ne [26], Ar [27], Kr [28], Xe [29] and Li [30], Na [31], K [32], Rb [32] atoms, and another two atoms are N [33] and Zn [34], respectively. Here, the experimental atomic polarisabilities of groups VIII and I are correlated with | R| R•F , respectively.…”

“…Some commonly accepted theoretical or experimental values of atomic polarisabilities are cited in Figure 6. Among them, the data of He [25], Ne [26], Ar [27], Kr [28], Xe [29], Li [30], Na [31], K [32], Rb [32], N [33], Zn [34], Al [41], Ca [42], Sr [43], In [44], Sn [45] and Cd [46] atoms come from experiments. The remaining data come from quantum mechanical calculations.…”

The CI calculation of the frequency-dependent polarizability and some optical properties for N2and O2

“…The index of refraction n of a gas in low pressure can be evaluated by n --1 = 2rrN~(hco), (15) where N is the number of molecules per unit volume. well, the refractive index of air can be estimated by volume-averaging the values of N 2 (78 vol per cent) and 0 2 (21 vol per cent).…”

ARTS, the atmospheric radiative transfer simulator – version 2.2, the planetary toolbox edition

“…Newell and Baird, 1965;Stratton, 1968), it can be 5 determined from the refractivity at reference conditions (pressure p ref and temperature T ref ) and applying a gas law to scale it to other conditions. For a gas mixture, the total refractivity can then be determined as the sum of all partial refractivities, i.e.…”

“…Reference refractivities of N 2 , O 2 , CO 2 , H 2 , and He, derived at 47.7 GHz and considered to be valid for microwave and sumbillimeter-wave frequencies, have been taken from Newell and Baird (1965). To achieve a better agreement with parametrisations for Earth, H 2 O is considered, too, and its reference refractivity has been estimated from the parametrisation by Thayer (1974).…”