Improved Molecular Constants for the Ground State of HO2

Molecular constants for the ground state of HO2 were recently published TABLE 2 by some of us (1) . These constants were based on measurements of the Revised Molecular Constants for the HO2 Ground State (MHz) frequencies of 17 transitions in the region 2.5 to 5.9 THz combined with Including Combination Differences from à A * r X̃ A 9 previously measured microwave and millimeter-wave measurements. Unfortunately it has been found that there was a small error in the computer program used; the off-diagonal spin–rotation matrix element »NKÉHSRÉN 0 1K ... included a term D NK N(N / 1)(K /2)(N 2 0 K ) f(N) instead of the correct D NKN (K /2)(N 0 K)f(N) . This error particularly affected the values fitted for bs , D NK , d K , and T 1 . Table 1 gives the molecular constants obtained after this correction. In the meantime, a rotational analysis of the 000–000 band of the à A* r X̃ A 9 electronic transition in the region of 7000 cm (2) revealed systematic discrepancies between observed and calculated ground state combination differences at high values of N and Ka . The terahertz, microwave, and millimeter-wave measurements encompassed rotational levels up to N Å 26 and Ka Å 5 but the nearinfrared measurements extended to N Å 31 and Ka Å 9. The magnitude of the discrepancy for predicting combination differences involving Ka Å 7– 9 was 0.01–0.04 cm . A revised set of molecular constants is obtained by combining both sets of data with appropriate weightings, where the combination differences are assigned uncertainties of 0.002–0.003 cm , and refitting to the parameterized Hamiltonian. Combination differences (133), involving values of N REFERENCES and Ka found only in the near infrared band, and 173 rotational transitions are used in the final fitting. The weighted RMS of the fit is 1.1. The revised 1. K. V. Chance, K. Park, K. M. Evenson, L. R. Zink, and F. Stroh, J. constants are given in Table 2. Mol. Spectrosc. 172, 407–420 (1995). 2. E. H. Fink and D. A. Ramsay, to be published.