Fourier Transform Emission Spectroscopy of the Visible Transitions of AuCl

Near-thermal reactions of Au(+)(1S,3D) with CH3X (X = F,Cl)

Reactions of Au(+)((1)S) and Au(+)((3)D) with CH(3)F and CH(3)Cl have been carried out in a drift cell in He at a pressure of 3.5 Torr at both room temperature and reduced temperatures in order to explore the influence of the electronic state of the metal on reaction outcomes. State-specific product channels and overall two-body rate constants were identified using electronic state chromatography. These results indicate that Au(+)((1)S) reacts to yield an association product in addition to AuCH(2)(+) in parallel steps with both neutrals. Product distributions for association vs HX elimination were determined to be 79% association/21% HX elimination for X = F and 50% association/50% HX elimination when X = Cl. Reaction of Au(+)((3)D) with CH(3)F also results in HF elimination, which in this case is thought to produce (3)AuCH(2)(+). With CH(3)Cl, Au(+)((3)D) reacts to form AuCH(3)(+) and CH(3)Cl(+) in parallel steps. An additional product channel initiated by Au(+)((3)D) is also observed with both methyl halides, which yields CH(2)X(+) as a higher-order product. Kinetic measurements indicate that the reaction efficiency for both Au(+) states is significantly greater with CH(3)Cl than with CH(3)F. The observed two-body rate constant for depletion of Au(+)((1)S) by CH(3)F represents less than 5% of the limiting rate constant predicted by the average dipole orientation model (ADO) at room temperature and 226 K, whereas CH(3)Cl reacts with Au(+)((1)S) at the ADO limit at both room temperature and 218 K. Rate constants for depletion of Au(+)((3)D) by CH(3)F and CH(3)Cl were measured at 226 and 218 K respectively, and indicate that Au(+)((3)D) is consumed at approximately 2% of the ADO limit by CH(3)F and 69% of the ADO limit by CH(3)Cl. Product formation and overall efficiency for all four reactions are consistent with previous experimental results and available theoretical models.

Experimental and theoretical studies of diatomic gold halides

The diatomic gold halides AuX are studied by means of Fourier-transform ion cyclotron resonance mass spectroscopy and ab initio theory at a quasi-relativistic CCSD(T) level of theory. A thermokinetic approach is used to determine the bond-dissociation energies of neutral AuCl, AuBr, and AuI as well as cationic AuI+, i.e., D(0)(Au-Cl) = 66 +/- 3 kcal/mol, D(0)(Au-Br) = 50 +/- 5 kcal/mol, as well as the brackets 52 kcal/mol < D(0)(Au-I) < 64 kcal/mol and 54 kcal/mol < D(0)(Au+-I) < 66 kcal/mol at 0 K. These values allow an evaluation of previous experimental and theoretical data concerning diatomic gold halides.

Pure rotational spectra, structures, and hyperfine constants of OC-AuX (X = F, Cl, Br)

Rotational spectra of OC-AuX (X = F, Cl, Br) have been measured in the frequency range 5-21 GHz, using a pulsed jet cavity Fourier transform microwave spectrometer. The molecules were prepared by ablating Au metal with a Nd:YAG laser and allowing the vapor to react with CO plus a halide precursor contained in the Ar backing gas of the jets. For OC-AuCl and OC-AuBr these are the first high-resolution spectroscopic measurements; for OC-AuF these are the first observations of any kind. All three molecules are linear. Rotational constants, centrifugal distortion constants, and nuclear quadrupole coupling constants have been precisely evaluated. The geometries determined for all three molecules show CO bond lengths close to that of free CO, plus relatively long Au-C bonds. These results are corroborated by ab initio calculations, which have also produced Mulliken populations showing significant sigma-donation from CO to Au, plus some pi-back-donation from Au to CO. There are major changes in the Au, Cl, and Br nuclear quadrupole coupling constants when CO bonds to AuX, consistent with the formation of strong Au-C bonds. The structural properties of OC-AuF are somewhat different from those of OC-AuCl and OC-AuBr.

Structural variations and bonding in gold halides: a quantum chemical study of monomeric and dimeric gold monohalide and gold trihalide molecules, AuX, Au2X2, AuX3, and Au2X6 (X = F, Cl, Br, I)

The molecular structures of all gold mono- and trihalides and of their dimers have been calculated at the B3LYP, MP2, and CCSD(T) levels of theory by using relativistic pseudopotentials for all atoms except fluorine. Our computations support the experimental observation that the relative stability of the monohalides increases from the fluoride toward the iodide, while the stability trend of the trihalides is the opposite. The potential energy surface (PES) of all gold trihalides has been investigated. These molecules are typical Jahn-Teller systems; the trigonal planar D3h-symmetry geometry does not correspond to the minimum energy structure for any of them. At the same time, the amount and character of their Jahn-Teller distortion changes gradually from AuF3 to AuI3. The minimum energy geometry is a T-shaped structure for AuF3 and AuCl3, with a Y-shaped transition-state structure. For AuI3, the Y-shaped structure lies lower than the T-shaped structure on the PES. For AuBr3 and AuI3, neither of them is the global minimum but instead an L-shaped structure, which lies outside the Jahn-Teller PES. This structure can be considered to be a donor-acceptor system, or a closed-shell interaction, with I2 acting as donor and AuI as acceptor. The dimers of gold monohalides have very short gold-gold distances and demonstrate the aurophilic interaction. The dimers of the trihalides are planar molecules with two bridging halogen atoms.

The Pure Rotational Spectra of AuCl and AuBr

The pure rotational spectra of AuCl and AuBr have been measured in the v = 0 and 1 (also for v = 2 for Au(35)Cl) vibrational states in the 5-22 GHz spectral region using a cavity pulsed-jet Fourier transform microwave spectrometer. The molecules were prepared by ablating Au metal in the presence of Cl(2) or Br(2) entrained in the Ar or Ne backing gas of the jet. The equilibrium internuclear distances r(e) have been determined along with estimates of the harmonic vibration frequencies and the dissociation energies. The ionic characters of the AuCl and AuBr bonds have been estimated from the halogen nuclear quadrupole-coupling constants to be i(c) approximately 38%. The gold nuclear quadrupole coupling constants change appreciably from AuF to AuCl to AuBr (including a sign change), indicating substantial differences in their electronic structures at Au; these variations could not be accounted for with a simple Townes-Dailey calculation. Copyright 2000 Academic Press.