Neutral rare-gas containing charge-transfer molecules in solid matrices. I. HXeCl, HXeBr, HXeI, and HKrCl in Kr and Xe

TLDR: In this article, the authors show the participation of rare gas atom(s) in these new compounds, based on studies of the thermally generated species in mixed rare gas matrices, and their vibrational spectra are discussed and compared with those calculated with ab initio methods.

Abstract: Ultraviolet‐irradiation of hydrogen halide containing rare gas matrices yields the formation of linear centrosymmetric cations of type (XHX)+, (X=Ar, Kr, Xe). Annealing of the irradiated doped solids produces, along with thermoluminescence, extremely strong absorptions in the 1700–1000 cm−1 region. Based on isotopic substitution and halogen dependence of these bands, the presence of hydrogen and halogen atom(s) in these species is evident. In the present paper we show the participation of rare gas atom(s) in these new compounds. The evidence is based on studies of the thermally generated species in mixed rare gas matrices. The new species are assigned as neutral charge‐transfer molecules HX+Y− (Y=halogen), and their vibrational spectra are discussed and compared with those calculated with ab initio methods. This is the first time hydrogen and a rare gas atom has been found to make a chemical bond in a neutral stable compound. The highest level ab initio calculations on the existence of compounds of type HXY corroborate the experimental observations. The mechanism responsible for the formation of these species is also discussed.

Figures

FIG. 5. The UMP2/LANL1DZ calculated potential energy surfaces for d ferent configurations of HXeCl. The open circles indicate the singlet surf with respect to the H–Xe bond length. At all H–Xe values the Xe–Cl bo distance was optimized. The filled circles show the triplet energetics ca lated at the corresponding singlet geometries.

TABLE IV. Ab initio calculated harmonic wave numbers of neutral HXY species at different levels. Numbers in parentheses are intensities~km/mol!.

FIG. 1. Photolysis of HI/DI in Xe~M/A;200!. The lowest trace shows the situation after deposition at 50 K~recorded at 15 K!, indicating almost equal amounts of H- and D-precursors. The middle trace is after Hg-arc irrad tion, showing complete photodissociation of the precursor. Annealing photolyzed matrix at 45 K yields the uppermost spectrum with basically t extremely intense bands. It is to be noted that all of the spectra shown drawn in the same absorbance scale.

FIG. 6. The UMP2/LANL1DZ-calculated energies of the different precurso combinations involved in the formation of HXeCl. The energies of the frag ments are calculated at infinite separation.

TABLE I. Thermally induced peaks in different H~D!Y/X matrices~Y5Cl, Br, I, X5Xe, Kr!. The main absorptions are underlined.

FIG. 3. Thermally induced absorptions of photolyzed HBr/Xe/Kr matrice A Xe concentration of 5% yields the band at higher wave numbers and concentration of Xe is 95% for the lower wave number spectrum. The sp tra are drawn on the same scale and in these experiments the amoun mixture deposited was the same.