The reaction of laser-ablated Al atoms and normal-H(2) during co-deposition at 3.5 K produces AlH, AlH(2), and AlH(3) based on infrared spectra and the results of isotopic substitution (D(2), H(2) + D(2) mixtures, HD). Four new bands are assigned to Al(2)H(4) from annealing, photochemistry, and agreement with frequencies calculated using density functional theory. Ultraviolet photolysis markedly increases the yield of AlH(3) and seven new absorptions for Al(2)H(6) in the infrared spectrum of the solid hydrogen sample. These frequencies include terminal Al-H(2) and bridge Al-H-Al stretching and AlH(2) bending modes, which are accurately predicted by quantum chemical calculations for dibridged Al(2)H(6), a molecule isostructural with diborane. Annealing these samples to remove the H(2) matrix decreases the sharp AlH(3) and Al(2)H(6) absorptions and forms broad 1720 +/- 20 and 720 +/- 20 cm(-1) bands, which are due to solid (AlH(3))(n). Complementary experiments with thermal Al atoms and para-H(2) at 2.4 K give similar spectra and most product frequencies within 2 cm(-1). Although many volatile binary boron hydride compounds are known, binary aluminum hydride chemistry is limited to the polymeric (AlH(3))( solid. Our experimental characterization of the dibridged Al(2)H(6) molecule provides an important link between the chemistries of boron and aluminum.

No abstract

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information ABSTRACTWe report spectroscopic observations on B atoms isolated in cryogenic parahydrogen (pH 2 ), normal deuterium (nD 2 ), Ne, Ar, Kr, and Xe matrices, and of B 2 molecules in Ne, Ar, Kr, and Xe matrices. The 2s 2 3s( 2 S) *--2s 2 2p( 2 P) B atom Rydberg absorption suffers large gas-tomatrix blue shifts, increasing from +3000 to +7000 cm-1 in the host sequence: Xe < Kr < Ar t Ne z nD 2 t pH 2 . Much smaller shifts are observed for the 2s2p 2 ( 2 D) +-2s 2 2p( 2 P) B atom coreto-valence transition. We assign pairs-of absorption peaks spaced by • 10 nm in the 315 to 355,*4 -------)egion to the B 2 (A 3Z," < X 3 Zg-) Douglas-Herzberg transition. We assign a much weaker 1•q'i,# progression in the 260 to 300 nrm region to the B 2 (2) l' --X + Z transition. We report a nove progression of strong peaks in the 180 to 200 nm region which we suspect may be due to B 2 molecules, but which remains unassigned. Ultraviolet (UV) absorption spectra of B/pH 2 solids show two strong peaks at 216.6 and 208.9 nm, which we assign to the matrix perturbed 2s 2 3s( 2 S) +-2s22p( 2 P) and 2s2p 2 ( 2 D) <-2s 2 2p( 2 P) B atom absorptions, respectively. This assignment is