A Chemical Compound Formed from Water and Xenon: HXeOH

Autor: Mika Pettersson, Leonid Khriachtchev, Markku Räsänen, and Jan Lundell
Rok vydání: 1999
Předmět:
Zdroj: Journal of the American Chemical Society. 121:11904-11905
ISSN: 1520-5126
0002-7863
Popis: Xenon is the most reactive stable rare gas, and its chemical properties have been widely explored since the discovery of the first xenon-containing compound by Bartlett in 1962.1,2 Usually, extremely electronegative substances are required to make a Xecontaining compound, and such reagents are seldomly found in nature, thus, allowing xenon chemistry only in the laboratory. Recently, we have shown that Xe and Kr can form neutral ground state HXY compounds, where X ) Xe or Kr and Y is a fragment with a relatively large electron affinity.3 One of the most profound examples is HXeSH synthesized in a low-temperature Xe matrix.4 The successful preparation of this compound prompted the search of its oxygen analogue, HXeOH. Here we report the preparation of HXeOH in a Xe matrix. This compound is unique because its preparation needs in addition to xenon only water, which is very abundant in nature, thus, shifting Xe chemistry from laboratory conditions toward environmental reality. In experiments, water vapor was mixed with xenon in a vacuum line roughly in a ratio Xe:H2O ) 1000 or larger. The gas mixture was deposited on a CsI substrate held at 30 K, which resulted in a highly monomeric matrix with respect to water. After deposition, the substrate was cooled to 7.5 K. Water molecules were dissociated in the matrix with a 193 nm ArF laser as demonstrated in Figure 1. The H2O f H + OH channel and subsequent permanent trapping of H atoms and OH radicals were confirmed by the observation of LIF (laser induced fluorescence) from HXen exciplexes and OH radicals.5,6 In addition, an IR band appeared at 3531.3 cm-1 which can be assigned to OH radicals in agreement with the assignment in ref 7. The OH concentration started to decay slowly after achieving a maximum, indicating that 193 nm photolyzes it to oxygen and hydrogen atoms. The rise of O atoms was monitored by LIF as well.8 After the decomposition of H2O and formation of H atoms and OH radicals, the matrix was annealed at two stages. First, the matrix was warmed to 35 K, and at this temperature O atoms are mobilized,9 as witnessed by appearing bands at 1383 and 1096 cm-1 (HO2), and ∼1027 cm-1 (O3). No changes in the waterbending region appear at this stage as seen in Figure 1. At the second stage, the matrix was warmed to about 48 K to mobilize H atoms. At this temperature XeH2 appeared indicating global diffusion of H atoms. In addition to known bands of XeH2 at 1166 and 1180 cm-1, a new strong absorption appeared at 1577.6 cm-1 after annealing at 48 K, as shown in Figure 1. This band does not belong to a water molecule, and it appears only after 193 nm photolysis and annealing at >40 K. Comparative experiments with H2O, HDO, and D2O were performed to identify the species responsible for the new absorptions, and the results are presented in Figure 2. Two different shifts for the new compound were observed. A new band at 1141.2 cm-1 indicates a D-shift for a hydrogen stretch with a H/D ratio of 1.382 from 1577.6 cm-1. The second band appeared at 1572.2 cm-1, suggesting that the molecule contains another hydrogen atom. Consistent with this, the strongly shifted band at 1141.2 cm-1 also had another slightly shifted counterpart at 1149.3 cm-1. When the H2O:HDO:D2O ratio was changed, the relative intensities of the four bands changed accordingly. For example, in a matrix with mostly HDO and D2O, the band at 1577.6 cm-1 was almost invisible. All four absorptions have smaller sidebands as seen in Figure 2. These bands are collected in Table 1. † E-mail: petters@csc.fi. (1) Bartlett, N. Proc. Chem. Soc. 1962, 218. (2) For a recent review, see: Holloway, J. H.; Hope, E. G. AdV. Inorg. Chem. 1999, 46, 51-100. (3) Pettersson, M.; Lundell, J.; Rasanen, M. Eur. J. Inorg. Chem. 1999, 729-737 and references therein. (4) Pettersson, M.; Lundell, J.; Khriachtchev, L.; Isoniemi, E.; Rasanen, M. J. Am. Chem. Soc. 1998, 120, 7979-7980. (5) Creuzburg, M.; Wittl, F. J. Mol. Struct. 1990, 222, 127-140. (6) Goodman, J.; Brus, L. E. J. Chem. Phys. 1977, 67, 4858-4865. (7) Pehkonen, S.; Pettersson, M.; Lundell, J.; Khriachtchev, L.; Rasanen, M. J. Phys. Chem. 1998, 102, 7643-7648. (8) Lawrence, W. G.; Apkarian, V. A. J. Chem. Phys. 1992, 97, 2229-2236. (9) Danilychev, A. V.; Apkarian, V. A. J. Chem. Phys. 1993, 99, 86178627. Figure 1. Photolysis and annealing of a H2O/Xe ) 1/2000 matrix: (a) situation after deposition showing the vibration-rotation bands of monomeric water; (b) situation after 104 pulses of 193 nm radiation showing the decomposition of ∼70% of water; (c) annealing of the matrix at 35 K mobilizes O atoms, which is evidenced by formation of ozone and HO2; (d) annealing at 48 K mobilizes H atoms, which is evidenced by formation of XeH2 and a new product marked with *; (e) selective bleaching of the band at 1577.6 cm-1 by irradiation with 355 nm for 5 min. All of the spectra are recorded at 7.5 K with 1 cm-1 resolution.
Databáze: OpenAIRE
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