Determination of the Hyperfine Structure in theAΣ122

Abstract

The hyperfine structure of OH in the ^4 2 2 1/^+ state has been measured by exciting a molecular beam with cw intracavity frequency-doubled dye-laser radiation. The splittings are 778 MHz for N' = 0 and 200 to 500 MHz for 1 *£ N' *s 5. The values for the hyperfine andp doubling are &+|c = 777.8±2.0 MHz, c -165.8±2.8 MHz, and y = 7.13± 0.03 GHz. Also the hyperfine splitting of OD in the N' =0 state has been measured yielding b + Jc = 119 ±2 MHz.The hydroxyl radical (OH) is one of the fundamental molecules in chemistry, physics, and astrophysics, It is the simplest diatomic openshell system, readily accessible for a wide range of spectroscopic techniques (optical, 1 infrared, 2 microwave, 3 and molecular beam-maser and -resonance 4,5 ) and accurate calculations. The radical plays an important role in laboratory and atmospheric chemistry and its maser emission in interstellar clouds forms a major unsolved problem in astrophysics,In the past considerable effort has been spent to unravel the structure and properties of OH a The structure of the ground electronic state (X 2 n), its vibrational and rotational levels, the p doubling, and the hyperfine structure are all well known. 6 This is, however, not the case for the first excited electronic state A 2 S 1/2 + where only the rotational and A-doubling energies are known from old optical work. The hyperfine structure due to the interaction between the magnetic moment 7=| of the hydrogen nucleus and the electronic spin has not been measured yet 0 In level-crossing experiments German et al 0 7 * 8 determined the hyperfine structure of OD in the A 2 S 1/2 + state from which they calculated the splittings for OH. The estimated values are on the order of 300 MHz which is beyond the resolution of conventional Doppler-limited spectroscopy (4 GHz at 300 K).The knowledge of the hyperfine structure is important not only for a theoretical understanding of the excited structure but also for the uv excitation models of interstellar OH radicals. As proposed by Litvak et al., 9 uv pumping might cause a population inversion between the A-doublet levels in the rotational ground state 2 n 3/2 , J=|, leading to the observed maser emissions. Turner 10 has

Analysis of measured high-resolution doublet rovibronic spectra and related line lists of 12CH and 16OH

“…Note that there are several outstanding papers which report highly accurate spin-rotation splittings within the A and C states of 12 CH 81,82 and the A 2 Σ + state of 16 OH. 71,72,122,127,130,136 For example, 86MeUbDy 136 contains hyperfine-resolved transitions between e/f doublets in the v = 0 vibrational state, 83MeMaM-eDy 130 contains similar data for both the v = 0 and v = 1 vibrational states of 16 OH, and 18FaFuMe 157 provides 12 highly accurate hyperfine-resolved transitions connecting the X and A states of 16 OH. of the hyperfine lines discussed here were employed during the MARVEL analysis of the large amount of hyperfineunresolved data.…”

“…Note that there are several outstanding papers which report highly accurate spin-rotation splittings within the A and C states of 12 CH 81,82 and the A 2 S + state of 16 OH. 71,72,122,127,130,136 For example, 86MeUbDy 136 contains hyperfine-resolved transitions between e/f doublets in the v = 0 vibrational state, 83MeMaMeDy 130 contains similar data for both the v = 0 and v = 1 vibrational states of 16 OH, and 18FaFuMe 157 provides 12 Table 6 Experimental sources used to construct the 12 CH hyperfine spectroscopic network. Given are the frequency range of the validated transitions of each source, the number of actual (A) and validated (V) transitions, and selected uncertainty statistics.…”

“…1 for the states covered in this study). To do this we analyze the experimental spectroscopic data available for the parent 12 CH 6,9–15,20,40,51,62–105 and 16 OH 8,21,31,38,41,43–47,52,53,106–158 isotopologues, using the Hamiltonian-free M arvel procedure, 1–5 and obtain high-accuracy empirical rovibronic energy levels with well-defined uncertainties. The empirical energy levels obtained allow the critical assessment of line lists 9,51–53 created previously for the two radicals.…”

High resolution electronic spectroscopy of Kr⋅OH/D and an empirical potential energy surface

“…This is a decrease of ϳ12% from the bare OH value. The Fermi contact parameter for bare OD was determined by ter Meulen et al 28 to be 119Ϯ2 MHz. A similar decrease to the Kr•OH complex would put the b value for Kr•OD about 105 MHz, well within our experimental linewidth, ϳ250 MHz, and hence explains our lack of observation of hyperfine structure in the deuterated complexes.…”