The photoabsorption and fluorescence cross sections of C2H2 were measured in the 50–106 nm region using synchrotron radiation as a light source. Fluorescence observed at several excitation wavelengths was dispersed to identify the fluorescing species that are excited C2H*, C*2 , CH*, H*, and possibly C2H+*2 . The photodissociation process of C2 H2 leading to the formation of fluorescing species is discussed. The C2 (C–A) emission observed at 92.3 and 95.5 nm is produced by the molecular elimination process associated with superexcited state(s). Fluorescence spectra from the two-photon excitation of C2 H2 at 157.5 and 193 nm were also observed and compared with those of single-photon excitation at the equivalent excitation energies.

Emission spectra of SiF3 radical were observed from photodissociative excitation of SiF4 at 99.1, 95.5, and 92.3 nm. The spectra show a broad visible band in the 350–800 nm region, a UV band in 290–340 nm, and a weak band in 240–280 nm. The visible band resembles the chemiluminescence spectra observed from etching of silicon by F or XeF2.

The absorption and fluorescence cross sections and the fluorescence quantum yields of BCl3 were measured in the 106–190 nm region. A visible emission band appears at excitation wavelengths shorter than 173 nm and two ultraviolet emission bands appear at wavelengths shorter than 126.5 nm. Fluorescence spectra were dispersed to identify emitting species that are attributed to BCl*2. The upper limits of the potential energies for the observed emitting states are 2.56, 5.19, and 5.70 eV, as determined from the fluorescence thresholds. The photodissociation process of BCl3 is discussed in accord with the fluorescence observed. The radiative lifetimes of the visible band vary over the 5–24 μs range, and the quenching rate constants of the excited state by BCl3 vary in (1.2–2.7)×10−10 cm3/s, both depending on fluorescence wavelength.

The photoabsorption, fluorescence cross sections, and the fluorescence yield of BC1 3 are measured in the 45-106 nm region. Fluorescence spectra are dispersed to identify the emitting species. The emission observed at excitation wavelengths longer than 96 nm is attributed to the excited BC1!. The BCl (A-X) emission appears at excitation wavelengths shorter than 97.5 nm. Emissions observed at the thresholds of 88 and 81 nm are attributed to the excited BCI 3 + • (C 2 A ~ and D 2E') states, respectively. Emissions from excited B* atoms appear in the 48-64 nm region. In the 88-96 nm region the maxima and minima ofthe fluorescence cross section are complimentary with those of the BCI 3 + ionization yield, indicating where superexcited state(s) exist that decay through competitive channels of fluorescence and autoionization.

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