Duncan A. Wild

The 35Cl−–H2 and 35Cl−–D2 anion complexes: Infrared spectra and radial intermolecular potentials

Rotationally resolved mid-infrared spectra of the 35Cl−–H2 and 35Cl−–D2 anion complexes are measured in the regions associated with the H2 and D2 stretch vibrations. The 35Cl−–H2 spectrum contains a single Σ–Σ transition assigned to the more abundant ortho H2 containing species. The corresponding 35Cl−–D2 spectrum consists of two overlapping Σ–Σ transitions whose origins are separated by 0.24 cm−1, and which are due to absorptions by complexes containing para and ortho D2. The spectra are consistent with linear equilibrium structures for Cl−–H2 and Cl−–D2, although zero-point bending vibrational excursions are expected to be substantial. Ground state vibrationally averaged intermolecular separations between Cl− and the diatomic center-of-mass are deduced to be 3.195±0.003 A (35Cl−–H2) and 3.159±0.002 A (35Cl−–D2). Vibrational excitation of the diatomic core profoundly affects the intermolecular interaction and leads to contractions of 0.118 A (35Cl−–H2) and 0.078 A (35Cl−–D2) in the vibrationally averaged...

Cl−–C6H6, Br−–C6H6, and I−–C6H6 anion complexes: Infrared spectra and ab initio calculations

Vibrational predissociation spectroscopy is used to obtain infrared spectra of the Cl−–C6H6, Br−–C6H6, and I−–C6H6 complexes in the region of the benzene CH stretch vibrations (2800–3200 cm−1). The infrared spectra of the three dimers are similar, each exhibiting several narrow bands (full width at half maximum <10 cm−1) that are only slightly redshifted from the absorptions of the free benzene molecule. Ab initio calculations predict that the most stable form of the three complexes is a planar C2v structure in which the halide is hydrogen bonded to two adjacent CH groups. The planar C2v structure in which the halide is linearly H bonded to a single CH group is predicted to be slightly less stable than the bifurcated form. Comparisons between experimental and theoretically predicted infrared spectra confirm that the bifurcated structure is indeed the most stable conformer for all three complexes. Ab initio calculations show that the electron density transfer from the halide to the benzene is not limited t...

Rotationally resolved infrared spectrum of the Cl−–H2 anion complex

The mid-infrared spectrum of the 37Cl−–H2 anion complex has been measured over the 3990–4050 cm−1 range (H–H stretch region) using infrared vibrational predissociation spectroscopy. The spectrum features a well resolved Σ–Σ transition red shifted by 156 cm−1 from the free H2 molecule stretch. Analysis of the P and R branch line positions using a linear molecule energy level expression yields ν0=4004.77±0.08 cm−1, B″=0.853±0.002 cm−1, D″=(9.3±1.0)×10−5cm−1, B′=0.919±0.002 cm−1, and D′=(9.0±1.0)×10−5 cm−1. The Cl−–H2 complex appears to have a linear equilibrium structure, with a vibrationally averaged separation of 3.19 A between the Cl− and the H2 center-of-mass. Vibrational excitation of the H–H stretch induces a 0.12 A contraction in the intermolecular bond.

Br−-H2 and I−-H2 anion complexes: Infrared spectra and radial intermolecular potential energy curves

Midinfrared spectra of the 81Br−-H2 and I−-H2 anion complexes are measured in the H-H stretch region by monitoring the production of halide anion photofragments. The spectra, which are assigned to complexes containing ortho H2, exhibit rotationally resolved ∑-∑ bands whose origins are redshifted from the molecular hydrogen Q1(1) transition by 110.8 cm−1 (Br−-H2) and 74.1 cm−1 (I−-H2). The complexes are deduced to possess linear equilibrium structures, with vibrationally averaged intermolecular separations between the halide anion and H2 center of mass of 3.461 A (Br−-H2) and 3.851 A (I−-H2). Vibrational excitation of the H2 subunit causes the intermolecular bond to stiffen and contract by 0.115 A (Br−-H2) and 0.112 A (I−-H2). Rydberg–Klein–Rees inversion of the spectroscopic data is used to generate effective radial potential energy curves near the potential minimum that are joined to long-range potential energy curves describing the interaction between an H2 molecule and a point negative charge. From the...

Rotationally resolved infrared spectrum of the Br−−D2 anion complex

The infrared spectrum of mass selected Li(+)-D(2) cations is recorded in the D-D stretch region (2860-2950 cm(-1)) in a tandem mass spectrometer by monitoring Li(+) photofragments. The D-D stretch vibration of Li(+)-D(2) is shifted by -79 cm(-1) from that of the free D(2) molecule indicating that the vibrational excitation of the D(2) subunit strengthens the effective Li(+)cdots, three dots, centeredD(2) intermolecular interaction. Around 100 rovibrational transitions, belonging to parallel K(a)=0-0, 1-1, and 2-2 subbands, are fitted to a Watson A-reduced Hamiltonian to yield effective molecular parameters. The infrared spectrum shows that the complex consists of a Li(+) ion attached to a slightly perturbed D(2) molecule with a T-shaped equilibrium configuration and a 2.035 A vibrationally averaged intermolecular separation. Comparisons are made between the spectroscopic data and data obtained from rovibrational calculations using a recent three dimensional Li(+)-D(2) potential energy surface [R. Martinazzo, G. Tantardini, E. Bodo, and F. Gianturco, J. Chem. Phys. 119, 11241 (2003)].

Infrared spectra of Cl−–(C2H2)n (1⩽n⩽9) anion clusters: Spectroscopic evidence for solvent shell closure

Mid-infrared vibrational predissociation spectra of mass selected Cl−–(C2H2)n (1⩽n⩽9) complexes have been recorded in the vicinity of the acetylene ν3 vibrational band (2700–3400 cm−1). For clusters containing up to 6 acetylene ligands, the spectra each feature a single dominant band, shifted to lower frequency from the ν3 C–H stretch band of free acetylene, and are consistent with interior solvation structures, whereby roughly equivalent acetylene molecules are bound end-on to a central chloride anion. Spectra of the n=7, 8, and 9 complexes, display multiple peaks and provide evidence for acetylene molecules situated in a second solvation shell and also for the existence of multiple isomeric forms. Depending on the cluster size, the inner solvation shell contains 6–8 acetylene molecules.

Infrared spectra of I−–(C2H2)n (1≤n≤4) anion complexes

Abstract Mid-infrared vibrational predissociation spectra of mass-selected I−–(C2H2)n (1≤n≤4) complexes have been recorded in the 2700–3400 cm−1 range. The spectra each feature a single compact band (fwhm≤40 cm−1), that is shifted from the ν3 C–H stretch band of free acetylene by −216.9, −176.7, −159.7 and −150.7 cm−1 for the n=1, 2, 3 and 4 clusters, respectively. The main absorption band of the I−–C2H2 dimer is consistent with a linear complex, in which excitation of the hydrogen-bonded C–H stretch induces a stiffening and contraction of the intermolecular I−⋯C2H2 bond. Spectra of the larger I−–(C2H2)n complexes are in accordance with structures where the I− is solvated by roughly equivalent hydrogen-bonded acetylene molecules.

Influence of P‐Bonded Bulky Substituents on Electronic Interactions in Ferrocenyl‐Substituted Phospholes

2,5-Diferrocenyl-1-Ar-1H-phospholes 3 a-e (Ar=phenyl (a), ferrocenyl (b), mesityl (c), 2,4,6-triphenylphenyl (d), and 2,4,6-tri-tert-butylphenyl (e)) have been prepared by reactions of ArPH2 (1 a-e) with 1,4-diferrocenyl butadiyne. Compounds 3 b-e have been structurally characterized by single-crystal XRD analysis. Application of the sterically demanding 2,4,6-tri-tert-butylphenyl group led to an increased flattening of the pyramidal phosphorus environment. The ferrocenyl units could be oxidized separately, with redox separations of 265 (3 b), 295 (3 c), 340 (3 d), and 315 mV (3 e) in [NnBu4 ][B(C6 F5 )4]; these values indicate substantial thermodynamic stability of the mixed-valence radical cations. Monocationic [3 b](+)-[3 e](+) show intervalence charge-transfer absorptions between 4650 and 5050 cm(-1) of moderate intensity and half-height bandwidth. Compounds 3 c-e with bulky, electron-rich substituents reveal a significant increase in electronic interactions compared with less demanding groups in 3 a and 3 b.

The Cl−–CH4 anion dimer: mid infrared spectrum and ab initio calculations

Abstract The Cl − –CH 4 dimer has been investigated using infrared vibrational predissociation spectroscopy (2800–3080 cm −1 range), and through ab initio calculations at the MP2(full)/aug-cc-pVTZ level. The infrared spectrum features parallel and perpendicular bands, associated with excitation of C–H stretch vibrations localized on the CH 4 core. Spectroscopic and theoretical data are consistent with a C 3v proton-bound minimum energy configuration for the complex, although internal rotation of the CH 4 sub-unit is not completely quenched. The calculated barrier for tunneling between equivalent proton-bound minima is 603 cm −1 . Comparisons are made between the properties of the isoelectronic Cl − –H 2 O, Cl − –NH 3 , and Cl − –CH 4 complexes.

Structural and energetic properties of the Br−–C2H2 anion complex from rotationally resolved mid-infrared spectra and ab initio calculations

An infrared vibrational predissociation spectrum of the 79Br−–C2H2 anion complex has been recorded over the 2800–3400 cm−1 range. Bands are observed that correspond to excitation of bound and free C–H stretches of an acetylene molecule engaged in a linear hydrogen bond with Br−. The band associated with the bound C–H stretch displays rotationally resolved substructure. Lower J transitions are absent from the predissociation spectrum, indicating that the upper levels lie below the dissociation threshold. Analysis leads to constants for lower and upper states: v0=2981.28, B″=0.048 84, ΔB=9.3×10−4 cm−1, and a minimum J′=28 for dissociation. The rotational constants correspond to vibrationally averaged separation between Br− and the C2H2 center of mass of 4.11 A in the ground state and 4.07 A in the v3 state. A dissociation energy for Br−–C2H2 of 3020±3 cm−1 is estimated from the energy of the lowest dissociating level. The spectroscopically derived data are corroborated by ab initio calculations conducted at...