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We have earlier determined the dependence on the bending angle of the interaction of the methylene radical (CH2) in its X3B1 state with He [L. Ma, P. J. Dagdigian, and M. H. Alexander, J. Chem. Phys. 136, 224306 (2012)]. By integration over products of the bending vibrational wave function, in a quantum close-coupled treatment we have calculated cross sections for the ro-vibrational relaxation of CH2(X). Specifically, we find that cross sections for a loss of one vibrational quantum (vb = 21 and 10) are roughly two orders of magnitude smaller, and those for a loss of two vibrational quanta (vb = 20) four orders of magnitude smaller, than those for pure rotational relaxation. In addition, no clear cut dependence on the energy gap is seen. [ABSTRACT FROM AUTHOR]

A microscopic Hamiltonian of the hydrogen-bond network in two-dimensional lattice water is proposed, which describes the formation and disruption of the H bonds, their bending, and which satisfies the Bernal–Fowler rules [J. D. Bernal and R. H. Fowler, J. Chem. Phys. 1, 515 (1933)]. The thermodynamic properties of the H-bond network are studied using the method of many-particle irreducible distribution functions, which is a generalization of the Kikuchi cluster approach [R. Kikuchi, Phys. Rev. 81, 988 (1951)] and the Bethe–Peierls quasiactivities method [H. A. Bethe, Prog. R. Soc. A 150, 552 (1935)]. The temperature dependencies of the average number of H bonds per molecules, the contribution of the H bonds into the heat capacity of the system, and the parameters describing the correlations between the states of molecules on the neighboring sites are investigated. It is shown that depending on the magnitude of the interaction between the H bonds in the H-bond subsystem either smooth or sharp first-order phase transition can occur. The role of different factors in the formation of the properties of the H-bond network is discussed. [ABSTRACT FROM AUTHOR]

The doubly degenerate core-excited Π state of N[sub 2]O splits into two due to the static Renner–Teller effect. The lower state, A[sub 1], has a bent stable geometry and the molecule excited to this state starts to deform itself toward this bent geometry. To probe the effect of the potential energy surfaces of the core-excited A[sub 1] states on the nuclear motion, we measure the momenta of the three atomic ions in coincidence by means of the ion momentum imaging technique. We find that the potential energy surface affects the molecular deformation significantly. N[sub 2]O in the terminal N 1s[sup -1]3πA[sub 1] excited state is observed to be bent more than that in the central N 1s[sup -1]3πA[sub 1] excited state. This means that N[sub 2]O in the terminal N 1s[sup -1]3πA[sub 1] excited state bends faster than that in the central N 1s[sup -1]3πA[sub 1] excited state. When the excitation energy is decreased within the 1s[sup -1]3π resonances, the nuclear motion in the A[sub 1] states becomes faster. This is interpreted by the notion that the excitation occurs onto the steeper slope part of the potential energy surface of the excited state for the lower excitation energy. The branching ratio of the A[sub 1] excitation increases with the decrease in the excitation energy. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We study the effects of asymmetric bending and twist rigidities and of spontaneous curvature and twist, on the statistical mechanics of fluctuating ribbons. Using a combination of Monte Carlo and differential geometry methods we perform computer simulations and calculate the probability density of the end-to-end distance of a ribbon. We find that for rectilinear ribbons of asymmetric cross section and for spontaneously curved rods with circular cross section, the distribution of end-to-end distance (but not its mean square) is affected by twist rigidity and by spontaneous twist. Possible relevance of these effects to the physics of DNA is discussed. [ABSTRACT FROM AUTHOR]

Investigates the floppiest bending modes of propadienone, butarienone and pentatetrenone with high quality ab initio methods. Determination of equilibrium molecular structures; Generation of the matrix-infrared spectra; Geometrical structures and barriers to chain linearity.

In a recent paper [J. Chem. Phys. 97, 4616 (1992)] that examines the relationship between experimental and computed intensities for bending modes of linear molecules, So\rensen and Jo\rgensen state that ‘‘most recent quantum mechanical computations predict band intensities of the bending modes in linear molecules that are approximately a factor of 2 bigger than observed intensities, and it is shown that the problem relates to the ab initio treatment.’’ It is further stated that ‘‘the disturbingly big discrepancies...are real, and the cause of the discrepancies has to be sought in the ab initio computation of the dipole moment.’’ This apparent failing of theory is addressed here by demonstrating that coupled-cluster calculations provide intensities for the bending modes of acetylene, carbon dioxide and nitrous oxide, of 177, 55, and 8 km/mol which compare favorably with the experimental values of 177, 55, and 7; while that for HCN is 70 compared to an experimental value of 58. The discrepancy in the latter might recommend some reconsideration of the experimental value, including the role of electrical and mechanical anharmonicity. [ABSTRACT FROM AUTHOR]

The torsional dependence of the CH[sub 3] stretching and bending modes of methanol has been explored in terms of a local mode internal coordinate picture [X. Wang and D. S. Perry, J. Chem. Phys. 109, 10795 (1998)]. First, the torsional variations of the small-amplitude vibrational frequencies along the mass weighted intrinsic reaction coordinate from the top to the bottom of the torsional potential barrier were calculated by means of ab initio frequency projection utilizing GAUSSIAN 98. The resulting curves for the three C-H stretch ab initio frequencies as functions of the torsional angle cannot be reproduced by the original 3x3 local mode model incorporating stretch-torsion and stretch-stretch couplings at lowest-order only, but are well-fitted if the model is extended to include higher-order coupling terms. For the CH-bending modes, with internal coordinates chosen to give a high degree of localization, bend-torsion and bend-bend coupling parameters were determined from the ab initio projected frequencies, and were then used to predict torsional tunneling splittings. Just as observed for the C-H stretch modes, the two higher-frequency asymmetric CH-bend modes are predicted to have inverted tunneling splittings with reduced amplitudes, while the splitting pattern for the lower frequency symmetric-bend mode is predicted to be normal. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]