Microwave Measurement ofD0for CO

Abstract

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

The band spectrum of carbon monoxide

“…Using a 6.5-m focal length grating with dispersion of 1.2 A/mm, he obtained the rotational structure of the 4-11, 5-13, 6-15, 7-16, 8-17, 9-19, 10-20, and 10-21 bands. Gero further reported [74] rotational structure for the 9-18, 11-20, 12-22, and [13][14][15][16][17][18][19][20][21][22][23][24] [74] believed that the appearance of these bands was due to accidental accumulation of lines, where strong overlapping is observed.…”