Adducts of Xenon with Organic Molecules: Rotational Spectrum of Dimethyl Ether–Xe

Abstract

KEYWORDS:gas-phase reactions ¥ noble gases ¥ rotational spectroscopy ¥ van der Waals adducts ¥ xenon Considerable interest has been devoted during the last two decades to the investigation of the rather unusual ™chemical compounds∫ formed by the combination of a noble gas atom with an organic molecule.[1] Various spectroscopic methods have been used to observe these adducts in the plume following a supersonic expansion.[2] Many van der Waals adducts between a noble gas atom and a cyclic organic molecule have been investigated by rotationally resolved spectroscopy, but only a very few involve a Xe atom: benzene ± Xe [3] and oxirane ± Xe [4] . The lack of experimental data on this kind of Xe complexes is probably due to the mass of Xe, which makes the rotational constants of its van der Waals complexes smaller than those of complexes of the lighter noble gases, and the large number of isotopes, with a maximum of natural abundance (27 %) for 132 Xe. Both factors considerably reduce the intensities of the rotational lines.Due to the higher polarizability of Xe relative to lighter noble gases, a larger dispersion ± energy interaction is expected for complexes with Xe. Here, we compare the stability and the dynamics of the noble gas atom in dimethyl ether ± xenon (DME ± Xe) to those of the related adduct oxirane ± Xe [4] and of the complexes of DME with Ne, Ar, and Kr, whose jet-cooled rotational spectra have been observed.[5±7] Figure 1 shows DME ± Xe and the van der Waals structural parameters.The first estimates of the rotational constants of the DME ± Xe were obtained by placing the xenon atom at a distance of 3.82 ä from the center of mass (CM) of DME, lying along the c axis of DME, but shifted by about 158 towards the oxygen atom, in a geometrical arrangement similar to that found for DME ± Ar [5] and DME ± Kr.[7] The r 0 geometry of DME [8] was assumed to Figure 1. Schematic diagram of DME ± Xe with van der Waals structural parameters.remain unaltered in the complex. On going from the molecule to the adduct the directions of the principal axes of inertia with respect to the C-O-C skeleton change, so that the m b -type spectrum of DME changes to a predominantly m c -type spectrum in the adduct (Figure 2). Figure 2. Switching of principal axes on going from DME to DME ± Xe.The rotational spectra of the two most abundant isotopic species, with 132 Xe and 129 Xe (ca. 27 and 26 % natural abundance, respectively), were investigated. Several high-J high-K a m c -R-type lines, doubly overlapping due to the near-prolate behaviour of K a , were easily assigned; later, the weaker lines with lower K a values, resolved into asymmetry doublets, were measured. The experimental frequencies (Table 1) were fitted with the Watson quartic Hamiltonian.[9] Since DME ± Xe is a near-prolate top, the S reduction and the I r representation were chosen. Three quartic centrifugal distortion parameters D J , D JK and D K were determined from the fit. The spectroscopic constants obtained are listed for both isotopomers in Table 2 together w...

Rotational Study of Dimethyl Ether–Chlorotrifluoroethylene: Lone Pair···π Interaction Links the Two Subunits

“…1 Coming back to the nonbonding interactions involved in the molecular complexes of DME, we can divide them in several categories. (i) van der Waals interactions characterize the adducts with rare gases, whose interaction energies are in the range 1.0−3.6 kJ/mol in going from DME−Ne 2 to DME−Ar, 3 DME−Kr, 4 and DME−Xe, 5,6 according to a linear dependence with the square of the rare gas atom polarizability. (ii) Weak hydrogen bonds of the type C−H•••O or C−H•••F (2 to 3 kJ/mol for each of them) link the subunits in the dimer of DME or in its adducts with hydrogen-containing freons.…”

“…Coming back to the nonbonding interactions involved in the molecular complexes of DME, we can divide them in several categories. (i) van der Waals interactions characterize the adducts with rare gases, whose interaction energies are in the range 1.0–3.6 kJ/mol in going from DME–Ne to DME–Ar, DME–Kr, and DME–Xe, , according to a linear dependence with the square of the rare gas atom polarizability. (ii) Weak hydrogen bonds of the type C–H···O or C–H···F (2 to 3 kJ/mol for each of them) link the subunits in the dimer of DME or in its adducts with hydrogen-containing freons. − (iii) Conventional hydrogen bonds have been found to constitute the main linkage with the partner molecule in complexes of DME with hydrogen halides , or alcohols. − In these complexes the dissociation energies have been estimated to be in the range 15–25 kJ/mol.…”

Internal Motions of the Rare Gas Atom in Dimethyl Ether−Krypton

“…From these splittings, the barriers to the rotation of the rare gas around dimethyl ether were estimated to be 0.19 and 0.69 kJ mol -1 , respectively. In the case of DME-Xe, no inversion splittings have been observed 1 Sketch of DME-Kr.…”

Infrared absorption spectroscopy of the CnXe (n = 2, 3, 5, 7, 9) species

“…16,28 Xenon has also been shown to form weakly bound complexes in solid rare gases with other compounds, such as HCl, CN, dimethyl ether, benzene, oxirane, and difluorovinylidene. [29][30][31][32][33] Theoretical studies on xenon-containing compounds have been reported over the past decade. H-Xe-R (R ¼ C 6 H 5 or other hydrocarbons) was predicted to be a stable species.…”