The theoretical and experimental analysis of fast passage phenomena in rotational spectroscopy is described in the pressure broadened limit. The phenomenon of Stark sweeping fast passage is carefully distinguished from the phenomena of transient absorption and transient emission that were treated earlier. We show that the observed response at the detector after Stark sweeping a molecular resonance through a fixed oscillator is a combination of off-resonance absorption and the beat between the fixed oscillator and the emission from the fast passage induced polarization.

A flash lanip is described in which electric discharge occurred transversely to the lamp axis between many electrode pairs. With an Hg vapour+He filling, the spectral emission was similar to that of a mercury resonance lamp. By positioning a small-diameter reaction vessel along the lamp axis, sufficiently high concentrations of transients were produced by Hg-flash-photosensitization for their detection by kinetic absorption spectroscopy. Relative yields of mercury hydride were nieasurcd in the reactions of Hg(63Pl,o) with H1, Dz and HD. With the latter, a marked preference for HgD formation was found. Comparison of the mercury hydride yields with predictions from a s1 atistical model showed that the transition complexes are too short-lived for energy partitioning to precede fragmentation. It is suggested that Hg(63P) attacks hydrogen molecules sideways on, and the preference for HgD formation may be a simple consequence of momentum conservation. Two possible potential surfaces for the reactions are discussed.

Infrared-microwave double resonance experiments on 13CH3F are described which lead to a direct measurement of T1, the relaxation time due to population differences for the two transitions J = 3 → J = 4; K = 3 and J = 4 → J = 5; K = 3 in the ground vibrational state. We find T1 = (10.5 ± 0.6) μsec mtorr. Comparing this work with low-power linewidth measurements which measure T2, the relaxation time of the induced polarization, indicates that T1 = T2 for the above two transitions. The theory used to interpret the experiments is developed starting from the density matrix formalism which leads to the electric dipole analog of the Bloch equations in nuclear magnetic resonance. The equations are solved for the conditions appropriate to this experiment which gives the results involving T1 and T2. The theory developed here should be of use in interpreting time-resolved infrared-microwave experiments in the future.

Stark switching microwave experiments on transient absorption and transient emission that allow the measurement of T1 and T2 in the J = 0→1 transition in OCS are described. The results from the transient absorption experiments are T1 = (26±4) × 10−6 sec · mtorr and T2 = (33±7) × 10−6 sec · mtorr. The results of the transient emission experiments give T2 = (31±3) × 10−6 sec · mtorr. Thus, T1 = T2 within the experimental uncertainties. We also demonstrate the effects of π/2 and π pulses by using Stark switching.

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