| dc.description.abstract | The techniques of matrix isolation spectroscopy have been employed in a study of the spectroscopy and structure of free radicals and molecules trapped in solid argon at low temperatures. Electronic transitions of several free radicals and molecules of astrophysical interest are reported: (a) The vacuum ultraviolet spectra of the products from the photolysis of acetylene C(,2)H(,2) trapped in Ar matrix at (TURN)8 K have been studied. The principal features of the observed spectra are two band systems appearing at 1600 and 1950 A. The band system at 1660 A is identified as the 3R-X Rydberg transition of the C(,4)H(,2) diacetylene molecule. It is proposed that the most likely assignment for the new band system at 1946 A is to the C(,2)H radical, and that the principal progression in 2175 cm('-1) and the shorter progression in 630 cm('-1) correspond to the (nu)(,2)' C(TBOND)C stretching mode, and even multiples 2(nu)(,2)' of the deformation mode. It is argued from simple molecular orbital considerations that the upper state of the 1946 A transition is (4(sigma)1(pi)('4)5(sigma)('2))('2)(SIGMA)('+), with C(,2)H retaining its linear geometry. (b) The absorption spectra of normal and deuterated diacetylene trapped in solid argon at 9 K have been investigated in the vacuum and near-ultraviolet region between 1200 and 3000 A. The vibrational structure observed at low temperature for the band system at 2448 A, which was previously reported by Haink and Jungen in the gas phase, and identified as a ('1)(DELTA)(,u)(<---)X('1)(SIGMA)(,g)('+) transition, has been analyzed. A comparison between the spectra for C(,4)H(,2) and C(,4)D(,2) suggests some revisions in the upper state vibrational assignments. The possibility that the upper state assumes a C(,2h) trans configuration of ('1)A(,u) symmetry has been examined. (c) The vacuum ultraviolet absorption spectrum to 1200 A has been obtained for the products from the evaporation of graphite at 2700 C, trapped in Ar at 8 K. Based on correlations with the ('1)(PI)(,u) - X('1)(SIGMA)(,g)('+) transition of C(,3) in the near ultraviolet, the results of ('13)C substitution, and other observational evidence, it is proposed that a new band system originating at 1890 A be assigned to the ('1)(SIGMA)(,u)('+) - X('1)(SIGMA)(,g)('+) transition of C(,3). | |
