Formation of HXeO in a xenon matrix: indirect evidence of production, trapping, and mobility of XeO (1(1)Sigma+) in solid Xe.

Abstract

IR spectroscopy, laser induced fluorescence (LIF), and thermoluminescence (TL) measurements have been combined to monitor trapping, thermal mobility, and reactions of oxygen atoms in solid xenon. HXeO and O(3) have been used as IR active species that probe the reactions of oxygen atoms. N(2)O and H(2)O have been used as precursors for oxygen atoms by photolysis at 193 nm. Upon annealing of matrices after photolysis, ozone forms at two different temperatures: at 18-24 K from close O ...O(2) pairs and at approximately 27 K due to global mobility of oxygen atoms. HXeO forms at approximately 30 K reliably at higher temperature than ozone. Both LIF and TL show activation of oxygen atoms around 30 K. Irradiation at 240 nm after the photolysis at 193 nm depletes the oxygen atom emission at 750 nm and reduces the amount of HXeO generated in subsequent annealing. Part of the 750 nm emission can be regenerated by 266 nm and this process increases the yield of HXeO in annealing as well. Thus, we connect oxygen atoms emitting at 750 nm with annealing-induced formation of HXeO radicals. Ab initio calculations at the CCSD(T)/cc-pV5Z level show that XeO (1(1)Sigma(+)) is much more deeply bound [D(e) = 1.62 eV for XeO --> Xe+O((1)D)] than previous calculations have predicted. Taking into account the interactions with the medium in an approximate way, it is estimated that XeO (1(1)Sigma(+)) has a similar energy in solid xenon as compared with interstitially trapped O((3)P) suggesting that both possibly coexist in a low temperature solid. Taking into account the computational results and the behavior of HXeO and O(3) in annealing and irradiations, it is suggested that HXeO may be formed from singlet oxygen atoms which are trapped in a solid as XeO (1(1)Sigma(+)).