Electronic Spectroscopy of B Atoms and B2 Molecules Isolated in Para-H2, Normal-D2, Ne, Ar, Kr, and Xe Matrices

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

Quantitative Absorption Spectroscopy of Aluminum Atoms in Cryogenic Parahydrogen Solids

“…We note in passing that we had previously tentatively assigned the 330 nm absorption in Al/H 2 samples to the 4s 2 S ← 3p 2 P 1/2 transition only, 7 leading to a factor of 0.295/0.115 ≈ 2.6× overestimation in our preliminary (unpublished 10 ) calculated Al-atom concentrations. Finally, as in our study of the B/pH 2 system, 14 we see no evidence in our UV spectra for metal dimers or larger pure metallic clusters. 37−39 The weak features in Figure 2 appearing near 380 nm are not reproduced in spectra of the same samples obtained using the tungsten-filament lamp source (not shown) and are probably artifacts caused by second-order diffraction of vacuum UV light (λ ≈ 190 nm) by the polychromator grating.…”

“…The correspondence between the distribution of gas-phase oscillator strength and the measured absorption spectrum is fairly good, with the notable exception of the 4s 2 S ← 3p 2 P 1/2 gas-phase transition at 394.4 nm (f ik = 0.115). 36 the B/pH 2 system, 14,15 we propose that this transition experiences a large gas-to-matrix blue-shift due to the large change in the radial extent of the electronic wavefunction that accompanies the increase in principal quantum number from n = 3 to 4. Conversely, we expect a much smaller shift of the 3d 2 D ← 3p 2 P 1/2 transition at 308.2 nm (f ik = 0.180), 36 for which Δn = 0.…”

“…Different aspects of our evolving apparatus have been described in detail before. 11,12,14,20,21 Here, we expand upon and consolidate these descriptions with appropriate citations and document the specific configuration used in the present experiments in sufficient detail to define our sample preparation protocol. Figure 1 shows a scale drawing of the apparatus, sectioned in the horizontal plane containing the most important sample preparation and diagnostic elements.…”

“…We retain our earlier spectroscopic assignments and calculated absorption coefficients for the Al x H y IR features 8 without any changes. We follow the photophysics model developed to explain the spectroscopy of boron atoms 14,15 in solid pH 2 to assign the Al/ pH 2 UV absorption spectrum. In addition to the familiar direct IR and UV absorptions, dopants in solid pH 2 induce additional IR activity in the host itself.…”

“…These components enable working to a short-wavelength cut-off of λ ≈ 180 nm. 14 We choose an intensified array detector and limit the D 2 lamp exposure times to minimize UV-induced photochemical reactions. 8 Unfortunately, this results in non-negligible intensity nonlinearities in the UV absorption data, which were not recognized in our earlier reports, 8,10 but which we address carefully below.…”