The relative intensities of 88 pairs of rovibrational transitions of OH (X 2Π) distributed over 16 vibrational bands (v′≤9, Δv=−1,−2) have been measured using Fourier transform infrared (FTIR) emission/absorption spectroscopy. Each pair of transitions originates from a common vibrational, rotational, and spin–orbit state, so that the measured relative intensities are independent of the OH number density and quantum state distribution. These data are combined with previous v=1←0 relative intensity absorption measurements and v=0, 1, and 2 permanent dipole moments to determine the OH dipole moment function as a cubic polynomial expanded about re, the equilibrium bond length. The relative intensities provide detailed information about the shape of the OH dipole moment function μ(r) and hence the absolute Einstein A coefficients. The intensity information is inverted through a procedure which takes full account of the strong rotation–vibration interaction and spin uncoupling effects in OH to obtain the dipole moment function (with 95% confidence limits): μ(r)=1.6502(2) D+0.538(29) D/Å (r−re)−0.796(51) D/Å2 (r−re)2−0.739(50) D/Å3 (r−re), 3 with a range of quantitative validity up to the classical turning points of the v=9 vibrational level (i.e., from 0.70 to 1.76 Å). The μ(r) determined in this study differs significantly from previous empirical analyses which neglect the strong effects of rotation–vibration interaction and spin uncoupling. The present work also permits distinguishing between the various ab initio efforts. Best agreement is with the dipole moment function of Langhoff, Werner, and Rosmus [J. Mol. Spectrosc. 118, 507 (1986)], but their theoretical predictions for higher overtone transitions are still outside of the 2σ experimental error bars. Absolute Einstein A coefficients from the present μ(r) are therefore presented for P, Q, R branch transitions for Δv=1, 2, 3, v′≤9, J′≤14.5, in order to provide the most reliable experimental numbers for modeling of near IR atmosphere OH emission phenomena.
A great deal of experimental effort has been put toward measurements of integral and differential, state-to-state cross-sections for rotationally inelastic energy transfer. Throughout the years measurements in thermal gas cells, and in crossed molecular beams, have been performed at increasingly impressive levels of quantum state detail. Because the term 'rotational energy transfer' can include collisional interchange among nuclear rotational states, magnetic sublevels, electron spin and orbital quantum levels, and vibrational angular momentum states, and can also include rotation-translationhibration energy transfer, the field is an expansive one. In this review an array of experimental studies is encapsulated, including discussion of quantum-state propensities, their known or speculative physical origins, and the success or failure of simple energy transfer models. Discussion of progress toward the development of accurate, jntermolecular potential energy surfaces, and the results of classical or quantum scattering calculations, accompanies the overview of experimental work.
Laser photolysis of HNO3 at 222 nm: Direct determination of the primary quantum yield of OH The absolute quantum yields (ct» for OH production from 193 and 248 nm photolysis of HN0 3 and H 2 0 2 are measured at room temperature using flash kinetic spectroscopy in a flow tube. The OH radicals are produced by excimer laser photolysis and probed via direct absorption of high resolution, tunable IR laser light. The resulting quantum yields are found to be <1>~~03 = 0.47 ± 0.06, <1>~i~2 = 1.22 ± 0.13, <1>:0 3 = 0.75 ± 0.10, and ct>~18°2 = 1.58 ± 0.23. These results indicate quantum yields for both precursors at both wavelengths which are less than the maximum possible values of 1 for HN0 3 and 2 for H 2 0 2 • The present measurements are discussed in light of contrasting results suggested from other work.
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