J. Phys. Chem. 1994, 98, 10375
Comment on the Hyperfine Structure of the X211 Ground State of Nitric Oxide
10375
TABLE 1: Comparison of Experimental Values of the Fermi Contact Interaction (b f c/3)and ab Initio Theoretical Values of the Nitrogen Isotropic Hyperfine Cou ling Constant A d N ) for the X2nGround States of 14N10 and 15N160
B
R. J. Miller* and David Feller
isotopic species
Pacific Northwest Laboratory, Richland, Washington 99352-0999
14Nl60
Received: May 16, 1994
F e m i contact interaction (b c/3), MHz 22.24" 22.52' -3 1.94" -31.56'
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theoretical
AsdN), MHz 18.4c,d 20 & 1"' -25.Sdf -28 & l'f
15N160 In their recent paper' describing results of theoretical investigations of the electronic and hyperfine structures of Reference 15. Reference 18. Reference 20. Multireference neutral nitrogen oxides, Eriksson, Wang, Boyd, and Lunell assert singles and doubles configuration interaction (MRSD-CI). e Estimated that the 52 = l/2 spin-orbit component of the X211 ground state full CI. fFeller, D. Unpublished results based upon ref 20. of NO does not have a direct hyperfine structure. The authors further state that their density functional theory (DFT) calculatiansen'* adopted this latter approach to obtain single sets of tions yield a state average of the density, therefore making it molecular parameters that simultaneously describe the Aimpossible to separate the 51 = l/2 and Q = 3/2 spin-orbit states doublings and the hyperfine structure splittings within both the and thus precluding an accurate determination of the hyperfine !2 = '12 and 52 = 3/2 spin-orbit components of the Xzll ground structure of the NO radical. state of NO. While the effective Hamiltonian operators It should be recognized, however, that 40 years ago Burms employed in these two analyses differ formally, the results of and GordyZ and Gallagher, Bedard, and Johnson3 utilized both can ultimately be cast in the familiar Frosch and Foley microwave spectroscopy to observe the J = 3/z J = VZ,pure magnetic hyperfine structure parameters a, b, c, and d.6,19Both rotational transition within Xzl11,2 14N160. In these investigatreatments therefore provide experimentally based values of the tions, both the A-doubling and the hyperfine structure were well Fermi contact interaction ( b c/3) which properly characterize resolved not only in the J = 3 / ~ state but also in the J = l/z the X z l l ground states of 14N160and 15N160and that can be state where the nuclear spin angular momentum of 14N splits compared directly to the results of ab initio theoretical calculathe lower energy, positive parity$,5 e-symmetry A-doublet level tionsZ0 of the nitrogen isotropic hyperfine coupling constant Aisoby *20 MHz and the higher energy, negative parity, fsymmetry A-doublet level by ~ 2 0 MHz. 5 At low J, the z l l ~ , ~(N) (Table 1). hyperfine structure is well described by Hund's case (up) References and Notes ~ o u p l i n g , ~and - ~ it, ~clearly exists even within @e no-motaiing (1) Eriksson, L. A.; Wang, J.; Boyd, R. J.; Lunell, S.J. Phys. Chem. molecule (R = O), that is, within J = l/2 where J R L 1994, 98, 792. S. Following these pioneering studies, the hyperfine structure (2) Burms, C. A,; Gordy, W. Phys. Rev. 1953, 92, 1437. of both the 52 = '12 and 51 = 3/2 spin-orbit components of (3) Gallagher, J. J.; Bedard, F. D.; Johnson, C. M. Phys. Rev. 1954, X211 14N160and 15N160have been scrutinized by a diversity 93, 729. of experimental techniques including microwave s p e c t r o s ~ o p y , ~ ~ ~ (4) de Vivie, R.; Peyerimhoff, S. D. J. Chem. Phys. 1989, 90, 3660. (5) Geuzebroek, F. H.; Tenner, M. G.; Kleyn, A. W.; Zacharias, H.; Zeeman'O and Stark" effect measurements, paramagnetic Stolte, S. Chem. Phys. Len. 1991, 187, 520. resonance spectro~copy,'~J~ molecular beam electric resonance (6) Frosch, R. A.; Foley, H. M. Phys. Rev. 1952, 88, 1337. (7) Townes, C. H.; Schawlow, A. L. Microwave Spectroscopy; methods,14J5and laser magnetic resonance spectroscopy.16The McGraw-Hill: New York, 1955; pp 196-199. zero-field hyperfine structure splittings within X2& NO even (8) Gallagher, J. J.; Johnson, C. M. Phys. Rev. 1956, 103, 1727. manifest themselves in Doppler-free fluorescence excitation (9) Favero, P.G.; Mini, A. M.; Gordy, W. Phys. Rev. 1959,114, 1534. (10) Mizushima, M.; Cox, J. T.; Gordy, W. Phys. Rev. 1955, 98, 1034. spectra of the (3sa)A2Z+ Rydberg state." (11) Bums, C. A.; Graybeal, J. D. Phys. Rev. 1958, 109, 1553. Spectroscopic data can certainly be used to define two distinct (12) Beringer, R.; Castle, J. G., Jr. Phys. Rev. 1950, 78, 581. sets of phenomenological constants that separately reproduce (13) Brown, R. L.; Radford, H. E. Phys. Rev. 1966, 147, 6. the energy level pattems of the two spin-orbit components of (14) Neumann, R. M. Astrophys. J . 1970, 161, 779. (15) Meerts, W. L.; Dymanus, A. J . Mol. Spectrosc. 1972, 44, 320. a 211state. It is preferable, however, to construct a single, (16) Mizushima, M.; Evenson, K. M.; Wells, J. S. Phys. Rev. A 1972, integrated model that in principle is capable of characterizing 5, 2276. all structural properties of the electronic state of interest. The (17) Miller, R. J.; Glab, W. L.; Bushaw, B. A. J. Chem. Phys. 1989, 91, 3277. resultant parameters provide a more physically significant (18) Kristiansen, P. J. Mol. Spectrosc. 1977, 66, 177. description of the various mechanical and magnetic properties (19) Dousmanis, G. C. Phys. Rev. 1955, 97, 967. of the molecule as well as a more unified and coherent treatment (20) Feller, D.; Glendening, E. D.; McCullough, E. A,, Jr.; Miller, R. J. of interstate perturbations. Meerts and Dymanusls and KrisJ . Chem. Phys. 1993, 99, 2829.
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0022-3654/94/2098-10375$04.50/0
0 1994 American Chemical Society
