A new and improved version of the technique of H atom photofragment translational spectroscopy has been applied to a study ofH 2 S photodissociation at 121.6 nm. The primary fragmentation pathways leading to H + SH(A) fragments and H + H + SeD) atoms are observed to dominate the product yield; the yield of H atoms formed in conjunction with ground state SH (X) fragments is undetectably small. The majority of the SH (A) fragments are formed in their v = 0 level with a rotational state population distribution that spans all possible bound and quasibound rotational levels. The experimental determination of the energies of these hitherto unobserved high rotational states has enabled a refinement of the SH(A) potential energy function, an improved estimate ofthe SH(A) well depth (9280 ± 600 cm-I ), and thus of the SH(X) ground state bond dissociation energy Dg (S-H) = 3.71 ± 0.07 eV. All aspects ofthe observed energy disposal in the title photodissociation process may be understood, qualitatively, if it is assumed that (i) the primary fragmentations occur on the B IAI potential energy surface and (ii) Flouquet's ab initio calculations of portions of this surface [Chern. Phys. 13, 257 (1976)] correctly predict its gross topological features.

Laser induced fluorescence Doppler spectroscopy has been applied for the first time to atomic hydrogen using tunable VUV light at the Lyman-e line. The dissociation of HI at 266 nm into H + I(P1/2) and H +I(P3/2) has been investigated. The recoil energy, angular distribution and branching ratio of the H atom have been measured, serving to test and study the feasibility and applicability of the technique.

Single rotational states were populated in vibrationally excited hydrogen by stimulated Raman pumping. The population in H2 X 1∑+g(v″=0,1) and D2 X 1∑+g(v″=0,1) was probed state selectively by tunable vacuum ultraviolet (VUV) laser radiation around λ=110 nm, and the fluorescence induced when exciting the hydrogen molecules in the (0–0), (1–0), (2–0), (3–1), and (4–1) Lyman bands of the (B 1∑+u←X 1∑+g) transition monitored. From a comparison of line heights, the stimulated Raman pumping efficiency is estimated to be 30%–50% in the focal volume. Rotational transitions in X 1∑+g(v″=1) were induced in collisions with H2, D2, and He. State-to-state rotational relaxation rates were measured for the (J″=1→J″=3) transition in H2(v″=1) and for the (J″=2→J″=0,4) transitions in D2(v″=1). These rates were found to be generally higher than the corresponding previously determined ones in ground state hydrogen, in qualitative accord with recent theoretical calculations. A comparison with available theoretical state-to-state cross sections shows that the rates obtained with these cross sections are generally lower than the relaxation rates directly measured in this work.

Selective photoionization from single rotational states of the B 1Σ+u(v′=0 and 3) excited state of the H2 molecule has been investigated with fixed frequency and tunable laser radiation around λ=266 nm. State selection of the B-state levels was achieved by tunable VUV laser excitation around λ=110 and 106 nm, respectively. The ionization cross section has been determined for different states, and found to be critically dependent upon the initial rotational quantum state and to show pronounced spectral structure with the ionization wavelength. At λI=266.05 nm the cross section varies between 0.23×10−18 and 1.2×10−18 cm2, depending on the initial state.

Die Infrarot‐ und Ramanspektren von Thioharnstoff‐Einkristallen bei 300 und 120°K werden mit polarisierter Strahlung aufgenommen. Zusätzlich werden die Spektren der deuterierten Verbindung an polykristallinen Proben und die Fern‐Infrarot‐Spektren an pulverförmigen Proben gewonnen. Damit ist eine vollständige Zuordnung der inneren und der Gitterschwingungen möglich. Durch Kopplung über zwischenmolekulare Kraftkonstanten und durch Dipol‐Wechselwirkung spalten die inneren Schwingungen um ca. 10 — 40 cm−1 auf. Die Umwandlung in die ferroelektrische Phase ist an Aufspaltungen, Intensitätsveränderungen und Frequenzsprüngen sichtbar. Aus den beobachteten Daten wird für den Bereich 25 bis 350 °K die Entropie berechnet, sie ist in guter Übereinstimmung mit experimentellen Werten.