Angular distributions are measured for individually resolved nu',j' states of HF produced by F + H-2 --> HF(nu' = 1, j') + H and F + H-2 --> HF(nu'=2,j') + H reactive collisions in a crossed-beams scattering apparatus. Simultaneous resolution of the HF vibrational and rotational states is achieved spectroscopically for the first time, using laser excitation in conjunction with bolometric detection. The technique is sensitive to population differences between nu' = 1,j' and nu' = 2,j' - 1 states optically coupled by specific P-2(j') lines of a vib-rotational chemical laser. The measurements are greatly facilitated by the development of a new high-temperature atomic fluorine beam source, which exhibits excellent stability, very high intensity, and narrow velocity distributions. Features common to individual product rotational states are as follows: strong backward scattering into nu' = 2,j'; weaker backward scattering into nu' = 1,j'; and heretofore unobserved scattering into nu' = 1,j' in the forward hemisphere. These angular distributions agree qualitatively with predictions from fully three-dimensional exact quantum reactive scattering calculations (Castillo et al., J. Chem. Phys. 1996, 104, 6531) that were conducted on an accurate potential energy surface (Stark and Werner, J. Chem. Phys. 1996, 104, 6515). However, quasi-classical calculations conducted on the same potential energy surface do not produce any substantial forward-scattered HF in nu' = 1 (Aoiz et al., Chem. Phys. Lett. 1994, 223, 215), suggesting that its appearance in the forward hemisphere may be a quantum effect. The quantum theoretical cross-sections also suggest that the forward nu' = 1 products arise almost entirely from H-2 reactants initially in j = 1.

Angular distributions for individually resolved ν, j states from the F+H2→HF(ν,j)+H chemical reaction are measured for the first time. Vibrational and rotational resolution is achieved simultaneously by applying laser+bolometer detection techniques to crossed-beam reactive scattering. In addition to backward-scattering HF(ν=1, j=6) and HF(ν=2, j=5), we also observe HF(ν=1, j=6) products scattered into the forward hemisphere. The results are in qualitative agreement with fully three-dimensional exact quantum reactive scattering calculations [Castillo et al., J. Chem. Phys. 104, 6531 (1996)] which were conducted on an accurate potential-energy surface [Stark and Werner, J. Chem. Phys. 104, 6515 (1996)]. However, the forward-scattered HF(ν=1, j=6) observed in this experiment is not reproduced by quasi-classical calculations [Aoiz et al., Chem. Phys. Lett. 223, 215 (1994)] on the same potential-energy surface.

Between Reformed Scholasticism and Pan-Protestantism: Jean-Alphonese Turretin (1671–1737) and Enlightened Orthodoxy at the Academy of Geneva. by Martin I. Klauber. Selinsgrove, N.J.: Susquehanna University Press, 1994. 244 pp. - Volume 65 Issue 1

view Abstract Citations (84) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Collisional Excitation of H 2O by H 2 Molecules Phillips, Timothy R. ; Maluendes, Sergio ; Green, Sheldon Abstract Using accurate theoretical rigid-rotor interaction potential for H2O-H2 and accurate coupled channel molecular scattering calculations, rates have been obtained for excitation of para- and ortho-H2O out of the lowest, j = 0, 1, and 2, rotational levels owing to collisions with para- and ortho-H2 at kinetic temperatures from 20 to 140 K. Excitation by para-H2 is not too different from excitation by He atoms, with most rates being within a factor of 1-3 larger, but excitation by is significantly different, with some rates an order of magnitude larger than rates for excitation by He atoms. Publication: The Astrophysical Journal Supplement Series Pub Date: November 1996 DOI: 10.1086/192372 Bibcode: 1996ApJS..107..467P Keywords: MOLECULAR DATA; MOLECULAR PROCESSES full text sources Publisher | ADS |

The close coupling formalism and the approximate coupled states formalism for collisions of an asymmetric top rigid rotor and a linear rigid rotor are reviewed. Calculations for excitation of H2O by H2 using a recent accurate, ab initio potential energy surface are presented.

Water (H2O) is fairly abundant in some regions of circumstellar and interstellar space. Maser emissions from a number of millimeter wave and microwave transitions are thought to be associated with interstellar regions near newly-forming stars, and near certain classes of late-type stars, such as Mira variables (Cohen 1989). Many other rotational transitions of water are difficult or impossible to detect from the Earth’s surface due to atmospheric H2O, and must be observed from high altitudes or must await the the availability of orbital telescopes such as the planned International Submillimeter Observatory and Submillimeter Wave Astronomical Satellite (SWAS). In any case, analysis of observations of H2O rotational transitions requires some knowledge of the behavior of the H2O molecule on collision with the most abundant interstellar and circumstellar species, hydrogen (H2) and helium (He). Theoretical studies of H2O-He collisions have been presented by Green (1980), and more recently by Palma et al. (1988, 1989) and by Green et al. (1993). Studies of H2O-H2 collisions are more complicated and have therefore been fewer, but one recent contribution has been made by Balasubramanian et al. (1993). Here we present the first results of our theoretical investigation of the H2O-H2 collision problem. We have calculated cross sections for the collisional 1(01)→1(10) excitation of ortho-H2O by ortho-and para-H2O using quantum-mechanical molecular collision theory as implemented in the MOLSCAT program (version 12, Hutson & Green 1993). The H2O and H2 molecules are considered to be rigid.

We have calculated the interaction for H2O–H2 at 722 points on a five-dimensional surface where both molecules are treated as rigid rotators and we have fitted the ab initio points to a 48-term angular expansion of products of spherical harmonics and rotation matrices. The resulting potential energy function shows strong angle dependence with a large contribution from electrostatic interactions. When averaged over H2 orientations, the resulting water-atom-like surface is found to have zero crossing and minimum at similar distances to the corresponding H2O–He surface but to be generally more repulsive at short range and more attractive at long range. The isotropic average of the potential has a zero-crossing radius σ=3.05 Å and a well depth ε=49.5 cm−1 at an intermolecular separation Rm=3.52 Å.

Reformierte Scholastik und Patristische Theologie: Die Bedeutung des Väterbeweises in der “Institutio Theologiae Elencticae” F. Turretins unter besonderer Beröcksichtigung der Gotteslehre und Christologie. By E. P. Meijering. Bibliotheca Humanistica & Reformatorica 50. Nieuwkoop, Netherlands:De Graaf Publishers, 1991. 507 pp. F 150. - Volume 62 Issue 4

An exhaustive search of the parameter space for the Ne–CH4 interaction potential is made in an attempt to determine a potential which will reproduce the results of molecular beam scattering experiments. The experiments were performed at low energy, well below the threshold for vibrational excitation. It is shown that the effects of the long-range part of the potential were not seen in the experiment. It is further shown that the anisotropy is well represented as far as the experiments are concerned by a fourth rank expansion. In the light of this and earlier studies, it is concluded that a rigid top model for methane is not capable of describing the experimental results even though the collision energy is well below the threshold for vibrational excitation. This is in marked contrast to atom–diatomic molecule scattering.