Mizuho TONOOKA (Nagoya Univ.), Satoshi YAMAMOTO (Univ. Tokyo), Kaori KOBAYASHI and Shuji SAITO
[J. Chem. Phys. 106, 2563 (1996)]
The NH2 radical is an important reaction intermediate in the hydrogenation of the nitrogen atom, and its physical and chemical properties have been studied by high-resolution spectroscopy. Among the various high-resolution spectroscopic methods, microwave spectroscopy is essential for precise determination of its hyperfine structure and, furthermore, line frequency determination for astronomical observations. We measured rotational spectra of the NH2 radical in its 2B1 ground electronic state by microwave spectroscopy in the frequency region of 230-470 GHz. The radical was generated in a free space cell by dc-glow discharge of NH3. Seventy nine fine and hyperfine components of four rotational transitions were measured and were analyzed by least squares methods. The hyperfine coupling constants for both the nitrogen and hydrogen nuclei were determined, as shown in Table 1, with higher precision than those of the previous analysis for microwave optical double resonance (MODR) data.1) The nuclear spin-rotation coupling constants for the hydrogen nucleus as well as the nitrogen nucleus were found to be anomalously large. The anomalous constant of Caa(H) is interpreted by the same reason as for the anomalous large value for Caa(N) originating from the large A constant and the relatively low-lying A2A1 electronic state, as first demonstrated in the study of ND2.2)
Table 1. Hyperfine Coupling Constants of the NH2(X2B1) Radicala
| Constant | Present study | LMR&MODRb |
| aF(N) | 28.061(52) | 28.2(4) |
| Taa(N) | -43.035(91) | -42.8(13) |
| Tbb(N) | -44.630(118) | -44.7(10) |
| caa(N) | 0.322(122) | 0.1(13) |
| cbb(N) | -3.809(141) | -1.6(11) |
| Caa(N) | 0.469(28) | |
| Cbb(N) | 0.114(24) | |
| Ccc(N) | 0.0228(96) | |
| aF(H) | -67.182(108) | -67.2(4) |
| Taa(H) | 18.217(174) | 18.6(13) |
| Tbb(H) | -13.05 (27) | -13.4(9) |
| Tab(H) | 58.5 c | |
| Caa(H) | 0.253(24) |
a MHz(3(sigma))
b Reference 1.
c T. C. Steimle, J. M. Brown and R. F. Curl, Jr., J. Chem. Phys. 73, 2352 (1980).