The results obtained from the microwave measurements of the rotational spectra of N 15 0 16 and N 14 0 16 in their 2 IIj ground state are compared by isotopic substitutions and shown to be in excellent agreement. The NO molecule is considered as an intermediate case, slightly removed from Hund's case (a). The theory of spin uncoupling and / uncoupling, developed by Van Vleck and extended by Dousmanis, Sanders, and Townes, is applied to the two molecules, and the molecular parameters are calculated accordingly. The resulting rotational constants are £ 0 =49 041.34 Mc/sec and Z> 0 =0.139 Mc/sec for N 15 0 16 , and £ 0 = 50 838.56 Mc/sec and Z>o=0.177 Mc/sec for N 14 0 16 . The A-doubling constants are found to have the following values: ^A = 170.45 Mc/sec for N 15 0 16 and 176.15 Mc/sec for N 14 0 16 ; and ?A=0.71 Mc/sec for N 15 0 16 and 1.15 Mc/sec for N 14 0 16 . The magnetic hyperfine structure is treated by an extension of the theory of Frosch and Foley to the intermediate case, and an expression is given for the quadrupole energy in the intermediate case. However, a very slight disagreement still exists between the measured and the calculated hyperfine separations.A complete list of the measured line frequencies is presented along with the calculated values. Also, a complete list of all of the molecular and nuclear parameters that have been determined is given.
Precise frequency measurements on rotational transitions occurring in the wavelength range from 2 to 3 mm for a number of molecules have been made. From these, centrifugal stretching effects have been determined and accurate values of the rotational constants obtained. A table including all frequencies so far measured in this region of the spectrum is given.
The value of D 0 for C 12 0 16 was determined as 189.0±0.7 kc/sec from measurements on the J = 0->\ and j=: 1->2 rotational transitions. Also, the frequency of the J= 1->2 line was determined as 230 536.59±0.52 Mc/sec. line, and the separation was thus given by twice the frequency of the modulating oscillator. 2 (The factor of two is due to the weak line being twice the frequency of the strong one.)The microwave energy at 1.3 and 2.6 mm was obtained from a crystal harmonic generator driven by a 1-cm Raytheon klystron. The absorption cell was a 7-foot length of silver waveguide 0.280X0.140 inches in cross section. The measurements were made at liquid air temperature, for which purpose the cell was encased in a brass tube insulated with two inches of styrofoam.The frequencies of the rotational transitions of a diatomic molecule in the ground vibrational state are:where J=0, 1, 2, • • •, B 0 = h/87r 2 cl 0 , and Do=4B 0 3 /co 2 . From this relation the frequency separation of the J=0-A and the'J=l->2 lines comes out to be 24Do. The measured value of 24Do obtained in this experiment is 4.535± 0.016 Mc/sec, thus giving a value of 189.0z±=0.rkc/sec or (6.30=1=0.03) XIO^6 cm" 1 for D 0 . This value is in fair agreement with D 0 =6.4 5 X10 _6 cm -1 obtained by Herzberg and Rao 3 from infrared data.The frequency of the J= 1->2 transition was found to be 230 536.59=1=0.52 Mc/sec by subtracting our value for 24D 0 from twice the measured frequency of the J=0->1 line (given asjl 15 270=1= 0.25 Mc/sec in reference 1).The measurement of D 0 is of value in the determination of the velocity of light by the method used by Rank 4 this molecule has been determined. Also, the frequency of the J= 1->2 transition was determined to a high precision by combining our measurement with the previously measured frequency of the J=0->1 transition. 1 Figure 1 shows an oscilloscope picture of the two CO absorption lines. The strong line on the right is the J=0->1 transition and the weaker line is the J= 1->2 transition. This type of picture was obtained by permitting microwave energy at 1.3-mm and also at 2.6-mm wavelength to pass through the absorption cell simul-FIG. 1. Oscilloscope picture of the J = 0->1 (right) and J= 1->2 (left) transitions of CO at liquid air temperature. The frequencies of the lines are 115 270.56 and 230 536.59 Mc/sec, respectively.taneously and be detected by one crystal. The separation between the two lines was measured by frequency modulating the klystron with a calibrated, variablefrequency oscillator to produce sidebands of the strong line. The first sideband was superimposed on the weak f
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