Showing papers by "Richard J. Saykally published in 1992"
TL;DR: A detailed experimental study of the water trimer shows a chiral six-membered ring structure with rapid quantum tunneling occurring between the enantiomers, speculated that larger water clusters would also exhibit transient chirality and that similar effects may be found in liquid water.
Abstract: A detailed experimental study of the water trimer is reported. A vibration-rotation-tunneling band of the perdeuterated cluster has been measured near 89.6 wave numbers by tunable far infrared laser absorption spectroscopy. The data indicate a chiral six-membered ring structure with rapid quantum tunneling occurring between the enantiomers. The observed vibration involves torsional motion of the water subunits about each hydrogen bond axis. It is speculated that larger water clusters would also exhibit transient chirality and that similar effects may be found in liquid water.
337 citations
TL;DR: In this article, a review of the information on both intramolecular forces and inter-molecular dynamics that has been obtained from far-infrared VRT spectra of 18 complexes during the past several years is presented.
Abstract: Measurements of the low-frequency van der Waals vibrations in weakly bound complexes by high-resolution laser spectroscopy provide a means to probe intermolecular forces at unprecedented levels of detail and precision. Several new methods are presently being used to record vibration/rotation-tunneling (VRT) transitions associated with the motions of the weak bonds in van der Waals clusters. The most direct measurements are those probing only the van der Waals modes themselves, which occur at far-infrared wavelengths. This article presents a review of the information on both intramolecular forces and intramolecular dynamics that has been obtained from far-infrared VRT spectra of 18 complexes during the past several years. Some rotationally resolved measurements of van der Waals modes observed in combination with electronic or vibrational excitation are also discussed. 185 refs., 15 figs., 1 tab.
118 citations
TL;DR: In this article, the authors have measured and assigned more than 800 new far-infrared absorption lines and 12 new microwave absorption lines of the ammonia dimer and analyzed all previously measured far infrared and microwave spectra for this cluster.
Abstract: We have measured and assigned more than 800 new far-infrared absorption lines and 12 new microwave absorption lines of the ammonia dimer. Our data are analyzed in combination with all previously measured far-infrared and microwave spectra for this cluster. The vibration–rotation–tunneling (VRT) states of the ammonia dimer connected by electric-dipole-allowed transitions are separated into three groups that correspond to different combinations of monomer rotational states: A+A states (states formed from the combination of two ammonia monomers in A states), A+E states, and E+E states. We present complete experimentally determined energy-level diagrams for the Ka=0 and Ka=1 levels of each group in the ground vibrational state of this complex. From these, we deduce that the appropriate molecular symmetry group for the ammonia dimer is G144. This, in turn, implies that three kinds of tunneling motions are feasible for the ammonia dimer: interchange of the "donor" and "acceptor" roles of the monomers, internal rotation of the monomers about their C3 symmetry axes, and quite unexpectedly, "umbrella" inversion tunneling.In the Ka=0 A+E and E+E states, the measured umbrella inversion tunneling splittings range from 1.1 to 3.3 GHz. In Ka=1, these inversion splittings between two sets of E+E states are 48 and 9 MHz, while all others are completely quenched. Another surprise, in light of previous analyses of tunneling in the ammonia dimer, is our discovery that the interchange tunneling splittings are large. In the A+A and E+E states, they are 16.1 and 19.3 cm^–1, respectively. In the A+E states, the measured 20.5 cm^–1 splitting can result from a difference in "donor" and "acceptor" internal rotation frequencies that is increased by interchange tunneling. We rule out the possibility that the upper state of the observed far-infrared subbands is the very-low-frequency out-of-plane intermolecular vibration predicted in several theoretical studies [C. E. Dykstra and L. Andrews, J. Chem. Phys. 92, 6043 (1990); M. J. Frisch, J. E. Del Bene, J. S. Binkley, and H. F. Schaefer III, ibid. 84, 2279 (1986)]. In their structure determination, Nelson et al. assumed that monomer umbrella inversion tunneling was completely quenched and that "donor–acceptor" interchange tunneling was nearly quenched in the ammonia dimer [D. D. Nelson, G. T. Fraser, and W. Klemperer, J. Chem. Phys. 83, 6201 (1985); D. D. Nelson, W. Klemperer, G. T. Fraser, F. J. Lovas, and R. D. Suenram, ibid. 87, 6364 (1987)]. Our experimental results, considered together with the results of six-dimensional calculations of the VRT dynamics presented by van Bladel et al. in the accompanying paper [J. Chem. Phys. 97, 4750 (1992)], make it unlikely that the structure proposed by Nelson et al. for the ammonia dimer is the equilibrium structure.
92 citations
TL;DR: In this paper, the vibration-rotation-tunneling (VRT) states of the NH3)2 complex were derived from microwave spectra and the potential used is a spherical expansion of a site-site potential which was extracted from ab initio data.
Abstract: In order to address the well‐known problem that the nearly cyclic structure of (NH3)2 deduced from microwave spectra differs greatly from the hydrogen‐bonded equilibrium structure obtained from ab initio calculations, we have calculated the vibration–rotation–tunneling (VRT) states of this complex, and explicitly studied the effects of vibrational averaging. The potential used is a spherical expansion of a site–site potential which was extracted from ab initio data. The six‐dimensional VRT wave functions for all the lowest states with J=0 and J=1 were expanded in products of radial (van der Waals stretch) functions and free‐rotor states for the internal and overall rotations, which were first adapted to the complete nuclear permutation inversion group G36. Although the (expanded) potential is too approximate to expect quantitative agreement with the observed microwave and far‐infrared spectra, we do find several interesting features: The 14N quadrupole splittings and the dipole moment of the complex, whic...
63 citations
TL;DR: In this article, a structure which is neither hexagonal nor cubic closest packed [space group P63/m, a= 33.54(1), c= 10.113(8)A] is described.
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= 33.54(1), c= 10.113(8)A]; packing models which are consistent with the Patterson map are described.
1 citations
TL;DR: In this article, a review of the information on both intramolecular forces and inter-molecular dynamics that has been obtained from far-infrared VRT spectra of 18 complexes during the past several years is presented.
Abstract: Measurements of the low-frequency van der Waals vibrations in weakly bound complexes by high-resolution laser spectroscopy provide a means to probe intermolecular forces at unprecedented levels of detail and precision. Several new methods are presently being used to record vibration/rotation-tunneling (VRT) transitions associated with the motions of the weak bonds in van der Waals clusters. The most direct measurements are those probing only the van der Waals modes themselves, which occur at far-infrared wavelengths. This article presents a review of the information on both intramolecular forces and intramolecular dynamics that has been obtained from far-infrared VRT spectra of 18 complexes during the past several years. Some rotationally resolved measurements of van der Waals modes observed in combination with electronic or vibrational excitation are also discussed. 185 refs., 15 figs., 1 tab.