Showing papers by "Richard J. Saykally published in 1991"
TL;DR: The role of intermolecular forces in modern science is becoming ever more prominent, as increasing numbers of chemists and physicists turn to the investigation of condensed matter phenomena and biological systems.
Abstract: The role of intermolecular forces in modern science is becoming ever more prominent, as increasing numbers of chemists and physicists turn to the investigation of condensed matter phenomena nd biological systems. Although thee subject is hardly novel, the state of our knowledge of intermolecular forces and their associated potential energy surfaces is, nevertheless, remarkably primitive. For example, isotropic descriptions of the pairwise interactions between most of the common small molecules have existed for many ears, but the anisotropy of these interactions still remains largely uncharacterized--even after nearly two decades of investigation with the most sophisticated experimental and theoretical techniques available! Furthermore, anisotropy is a dominant feature of systems that have the most significance, viz. those exhibiting hydrogen bonding. This state of affairs seems all the more surprising when one considers that detailed theoretical formulations have been developed (1) for describing the three types of weak attractive interactions that occur between a pair of molecules, viz. electrostatic, induction, and dispersion forces, and that at least the low-order parameters that describe these interactions (polarizabilities, dipole moments, quadrupole moments) are generally wellknown. However, as we elaborate upon in this review, it is our lack of
97 citations
TL;DR: In this paper, the first infrared spectrum of gas phase, jet-cooled C4 has been measured by high resolution diode laser absorption spectroscopy and 12 rovibrational transitions are assigned to the nu3(sigmau) antisymmetric stretch of linear 3Sigma -g C4.
Abstract: The first infrared spectrum of gas phase, jet-cooled C4 has been measured by high resolution diode laser absorption spectroscopy. Twelve rovibrational transitions are assigned to the nu3(sigmau) antisymmetric stretch of linear 3Sigma - g C4. No evidence is observed for the bent structure of triplet C4 recently observed in a matrix study by Cheung and Graham [J. Chem. Phys. 91, 6664 (1989)]. Indeed, the measured band origin (1548.9368(21) cm^–1) and effective ground state C–C bond length [1.304 31(21)A] are consistent with several ab initio predictions of a rigid, linear, cumulenic structure for this cluster radical.
97 citations
TL;DR: In terms of energy, photons in this region (0.03-1.0 kcal/mole) are less energetic than essentially all known hydrogen bond (and, of course, chemical bond) strengths but are about the same magnitude as typical van der Waals bond strengths as mentioned in this paper.
Abstract: Defined most conveniently in terms of modern technology, the far infrared (FIR) region of the spectrum extends from the frequencies where “standard” submillimeter techniques begin to fail ( - 10 cm - ’ = 0.3 THz) to those where lead-salt infrared diode laser technology becomes operative ( -350 cm- ’ = 10.5 THz). In this frequency range, pure rotational spectra of light molecules and torsional (hindered rotation) spectra of nonrigid molecules have been studied for many years. In terms of wavelength, this spectral region (30-1000 ,um) is centered near the peak of the room temperature (3-300 K) blackbody emission spectrum, and has accordingly been of great importance in the development of modern physics. In terms of energy, photons in this region (0.03-1.0 kcal/mole) are less energetic than essentially all known hydrogen bond (and, of course, chemical bond) strengths, but are about the same magnitude as typical van der Waals bond strengths. The extremely high resolution ( > 1 x 106) tradition
95 citations
TL;DR: In this article, a tunable far infrared laser spectrometer based on frequency mixing of an optically pumped molecular gas laser with tunable microwave radiation in a Schottky point contact diode is presented.
Abstract: A detailed description is presented for a tunable far infrared laser spectrometer based on frequency mixing of an optically pumped molecular gas laser with tunable microwave radiation in a Schottky point contact diode. The system has been operated on over 30 laser lines in the range 10–100 cm^–1 and exhibits a maximum absorption sensitivity near one part in 10^6. Each laser line can be tuned by ±110 GHz with first-order sidebands. Applications of this instrument are detailed in the preceding paper.
92 citations
TL;DR: The AW1 intermolecular potential surface as mentioned in this paper incorporates much of the essential physics of the intermolescular forces which bind the cluster and provides strong evidence that the AW1 as mentioned in this paper is a good fit to previous far-infrared spectral data.
Abstract: Five new vibration–rotation tunneling states of Ar–H2O [the Σ and Π(111) and the Σ and Π(212) internal rotor states and the n=1, Π(101) stretching‐internal rotor combination level] have been accessed by tunable far‐infrared laser spectroscopy. The measured vibrational band origins of transitions to these states are within 2% of predictions made from an anisotropic three‐dimensional intermolecular potential surface (denoted AW1) derived from a nonlinear least‐squares fit to previous far‐infrared spectral data [J. Phys. Chem. 94, 7991(1990)]. This provides strong evidence that the AW1 intermolecular potential surface incorporates much of the essential physics of the intermolecular forces which bind the cluster. However, larger deviations from the predictions are found in the observed rotational term values. A detailed analysis of these deviations clearly demonstrates the need for even stronger angular‐radial coupling in the Ar–H2O intermolecular potential than the already substantial coupling present in the...
72 citations
TL;DR: In this article, the bending potential of the v4 hot bands associated with the I (IT, I) bending fundamental has been characterized and the magnitude of these changes indicates extremely large amplitude bending motion about the central carbon atom.
Abstract: bending hot bands associated with the v4 fundamental. This constitutes the first characterization of the bending potential of C, . Excitation to u = 1’ of the Y, I (IT,, ) bending fundamental is accompanied by a huge increase (9.3%) in the rotational constant. Excitation from v = 1’ to v = 2’ of Y,~ results in an even larger increase ( 10.4%) in the rotational constant. The magnitude of these changes indicates extremely large amplitude bending motion about the central carbon atom, evidencing the predicted nonrigidity of C, . In addition, the v4 rotational transitions have been measured with improved precision and extended to
71 citations
TL;DR: In this article, two new intermolecular vibration-rotation-tunneling (VRT) bands of Ar-NH3 have been measured using tunable far infrared laser spectroscopy.
Abstract: Two new intermolecular vibration–rotation‐tunneling (VRT) bands of Ar–NH3 have been measured using tunable far infrared laser spectroscopy. We have unambiguously assigned these and a previously measured FIR band [Gwo et al., Mol. Phys. 71, 453 (1990)] as Π(10, n=0)←Σ(00, n=0), Σ(10, n=0)←Σ(00, n=0), and Σ(00, n=1)←Σ(00, n=0). The three upper states of these are found to be strongly mixed by anisotropy and Coriolis effects. A simultaneous least squares fit of all transitions has yielded vibrational frequencies, rotational and centrifugal distortion constants, and a Coriolis parameter as well as quadrupole hyperfine coupling constants for the upper states. An effective angular potential energy surface for Ar–NH3 in its lowest stretching state has been determined from these data, after explicitly accounting for the effects of bend stretch interactions. Features of the surface include a global minimum at the near T‐shaped configuration (θ=90°), a 30 cm−1 to 60 cm−1 barrier to rotation at θ=180° (or 0°), and a...
61 citations
TL;DR: The first far infrared intermolecular vibration-rotation spectrum of the ternary van der Waals cluster has been measured near 39.5 cm−1 and assigned to an a • type ∑ bending vibration of Ar2HCl as discussed by the authors.
Abstract: The first far infrared intermolecular vibration–rotation spectrum of the ternary van der Waals cluster has been measured near 39.5 cm−1 and assigned to an a‐type ∑ bending vibration of Ar2HCl. Spectra of both chlorine isotopes were observed and nuclear quadrupole hyperfine structure was resolved. Values of the fitted constants (rotational constants, hyperfine projections) evidence large amplitude out‐of‐plane motion, and demonstrate the sensitivity of spectroscopic observables to the three body forces operative in the Ar2HCl system. Spectroscopic predictions calculated by Hutson et al. from pairwise‐additive and ‘‘three‐body’’ corrected potential energy surfaces [J. Chem. Phys. 90, 1337 (1989)] are compared to experimental results.
46 citations
TL;DR: A second Ar2HCl intermolecular vibration-rotation band centered at 37.2 cm−1 has been measured and assigned as a b-type transition originating from the ground state.
Abstract: A second Ar2HCl intermolecular vibration–rotation band centered at 37.2 cm−1 has been measured and assigned as a b‐type transition originating from the ground state. Nuclear hyperfine splittings were resolved for both chlorine isotopes. The rotational constants determined from the data indicate coupling between an Ar–Ar stretching or bending coordinate and the Ar2 –HCl vibrational coordinates. As a result of this particular vibrational motion, Ar2H 35Cl undergoes an axis‐switching transition while the Ar2H 37Cl isotope does not. In addition, the measured hyperfine projections indicate the possibility of coupling between the Ar2 –HCl stretching and bending modes, preventing an absolute vibrational assignment. These results indicate that the ‘‘reversed adiabatic’’ approximation employed by Hutson, Beswick, and Halberstadt in their theoretical study of Ar2HCl [J. Chem. Phys. 90, 1337 (1989)] is not appropriate for the complicated intramolecular dynamics presently observed in this system.
36 citations
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TL;DR: In this article, the authors measured the 24 rotational lines associated with the ν 5 (σ u ) antisymmetric stretch vibration of C 7 have been measured by high resolution diode laser absorption spectroscopy of a supersonic carbon cluster beam.
33 citations
TL;DR: In this paper, a qualitative vibration-rotation tunneling energy level diagram is presented, which is consistent with the following assumptions: G36 is the appropriate molecular symmetry group; the equilibrium structure contains a plane of symmetry; interchange tunneling of inequivalent monomers occurs via a trans path; the 2C3+I limit of hydrogen exchange tunneling is appropriate; tunneling and rotational motions are separable.
Abstract: Over 150 lines in six tunneling subbands of an intermolecular vibration located near 25 cm−1 have been measured with partial hyperfine resolution and assigned to (NH3)2. The transitions sample all three types of tunneling states (A, G, E) and are consistent with the following assumptions: (1) G36 is the appropriate molecular symmetry group; (2) the equilibrium structure contains a plane of symmetry; (3) interchange tunneling of inequivalent monomers occurs via a trans path; (4) the 2C3+I limit of hydrogen exchange tunneling is appropriate; (5) tunneling and rotational motions are separable. A qualitative vibration–rotation tunneling energy level diagram is presented. Strong perturbations are observed among the states of E symmetry. This work supports the conclusions of Nelson et al. [J. Chem. Phys. 87, 6365 (1987)].
TL;DR: In this article, a structure which is neither hexagonal nor cubic closest packed [space group P63/m, a= 3354(1), c= 10113(8)A] was shown to be consistent with the Patterson map.
Abstract: Crystallographic analysis of C60 grown from a hexane solution revealed a structure which is neither hexagonal nor cubic closest packed [space group P63/m, a= 3354(1), c= 10113(8)A]; packing models which are consistent with the Patterson map are described
TL;DR: The trifluorovinyl radical (C 2 F 3 • ) was identified by using infrared spectroscopy as discussed by the authors, which was generated from UV laser photolysis.
Abstract: The trifluorovinyl radical (C 2 F 3 • ) is identified by using infrared spectroscopy. Real-time broadband infrared laser and diode infrared laser absorption spectra of the trifluorovinyl radical were measured. The radical was generated from UV laser photolysis of trifluoroiodoethene (C 2 F 3 I) at 248 nm in the gas phase. Pseudo-first-order decay kinetics of the transient vibrational bands were observed. Analysis of the photoproducts with Fourier transform infrared spectroscopy showed that 1,3-hexafluorobutadiene (C 4 F 6 ) was present in high concentration. It was probably formed from the reaction of trifluorovinyl radical with trifluoroiodoethene, as is consistent with the observed kinetics
TL;DR: In this paper, the osmate ester (2:1 adduct) was added to C60 without disrupting the carbon framework, and it was shown that oxygen functionality can be added without damaging the carbon structure.
Abstract: Treatment of C60 with osmium tetroxide and pyridine gives the osmate ester (2:1 adduct) establishing that oxygen functionality can be added to C60 without disrupting the carbon framework.