Microwave Spectra of the Free Radicals OH and OD

Abstract

Experiments are reported on the microwave spectra of the free OH radical. The radicals are produced by an electric discharge in concentrations near 10% at pressures of approximately 0.1 mm Hg. The spectra are detected by Zeeman modulation. They are due to direct transitions between the A-doublet levels of each rotational state in the ground vibrational level of the molecule. Spectra due to 0 16 H, 0 18 H, and 0 16 D in II* and II* states have been observed in the 7.7 to 37 kMc/sec region. Intensity of the lines ranges from about 5X10~~6 cm"" 1 to 5X10 -8 cm"" 1 .Van Vleck's theory of molecular energies in 2 n and 2 S states is extended to include terms of order (E vo t or Ef s ) 2 /E e i 2 . The experimental results are in agreement with theoretical expectations to about one part in 2000 which is the order of accuracy of the theory. An improved agreement (to one part in 3500) is obtained if one allows a small variation (one part in 1400) of the electronic wave function from one rotational state to the next. The values of the molecular constants determined from the A-type doubling data are 4 2 (-l)*(n|4i y +2BZ y |S>(S|5L I ,|n>/(fe-£n) 2-states = -2361.37±2.95 Mc/sec in 0 16 H and -1548.99±2.10 Mc/sec in 0 16 D; 4 S (-l) s |(n|5L 2/ |S>| 2 /(^s-^n) = 576.18±1.64 Mc/sec S-states in 0 16 H and 161.94zbl.61 Mc/sec in 0 16 D; A/B = -7.444±0.017 in 0 16 H and -13.954±0.032 in O l6 D. The spectra include magnetic hyperfine structure from which the following values are obtained for parameters that describe the unpaired electron distribution in the molecule: and (1A 3 )AV= (0.75±0.25)X10 24 cm"* (sin 2 xA 3 )Av= (0.49±0.01) X10 24 cm~The hyperfine structure, the molecular magnetic moment and the line intensities are strongly dependent on the extent of intermediate coupling in agreement with theoretical expectations. The microwave spectrum can be used in studying chemical properties of the radical. Its lifetime was determined to be near J sec, and the effects of certain substances on radical concentration were examined.

Detection of OD towards the low-mass protostar IRAS 16293−2422

“…Each component of the doublet is further split by the magnetic hyperfine structure (hfs) due to the deuterium atom into components characterised by the total angular momentum F(= J + I). F takes values of J − 1, J and J + 1 (Dousmanis et al 1955). The selection rule of ΔF = 0, ±1 leads to six hfs lines (Fig.…”

A Physicist Courts Astronomy

“…Discussions of these possibilities with one of my students, Alan Barrett, led him to decide he wanted to go into radio astronomy and look for astronomical sources of OH after he finished his degree. Some of my other students and Art Schawlow, who was then a postdoc, had obtained the OH spectrum in the microwave region in our laboratory at Columbia, so we had a reasonably good value for the OH frequency (Dousmanis et al 1955). Alan gave it a good try by taking a postdoctoral position with the radio xix astronomy group at the Naval Research Laboratory (NRL).…”

From High-Resolution Spectroscopy to Chemical Reactions

“…I thought that if we could apply microwave spectroscopy to this problem, we would get more detailed information on transient mol ecules than we would by using electronic spectroscopy. Up to 1960, only two transient molecules were detected by microwave spectroscopy: OH by Townes and coworkers (15) and CS by Mockler & Bird (16). Tn the US and Canada, I visited three microwave laboratories, which had been involved in similar projects: those of Rollie Myers at Berkeley, David Lide at the National Bureau of Standards Washington, and C. C. Costain at NRC Canada.…”