Pressure Effects on the Relaxation of an Excited Ethane Molecule in High-Pressure Bath Gases.

We use molecular dynamics to calculate the rotational and vibrational energy relaxation of CH in Ar, Kr, and Xe bath gases over a pressure range of 10-400 atm and at temperatures of 300 and 800 K. The CH is instantaneously excited by 80 kcal/mol randomly distributed into both vibrational and rotational modes. The computed relaxation rates show little sensitivity to the identity of the noble gas in the bath.

Force Based Canonical Approximation of Molecular Potentials: Average Force versus Pointwise Force.

This work presents a new force-based canonical approach that utilizes the average force rather than the pointwise force, on which previously developed canonical approaches were based. Advantageously, the average force based method only requires the evaluation of the potential function and not its derivative. The average force and the pointwise force based methods are applied to a variety of diatomic molecules, and their accuracy is compared.

Normal mode analysis on the relaxation of an excited nitromethane molecule in argon bath.

In our previous work [Rivera-Rivera et al., J. Chem.

Canonical Approach To Generate Multidimensional Potential Energy Surfaces.

A new force-based canonical approach for the accurate generation of multidimensional potential energy surfaces is demonstrated. Canonical transformations previously developed for diatomic molecules are used to construct accurate approximations to the 3-dimensional potential energy surface of the water molecule from judiciously chosen (adopting the right coordinate system) 1-dimensional planar slices that are shown to have the same canonical shape as the classical Lennard-Jones potential curve. Spline interpolation is then used to piece together the 1-dimensional canonical potential curves, to obtain the full 3-dimensional potential energy surface of a water molecule with a relative error less than 0.

Is there any fundamental difference between ionic, covalent, and others types of bond? A canonical perspective on the question.

The concept of chemical bonding is normally presented and simplified through two models: the covalent bond and the ionic bond. Expansion of the ideal covalent and ionic models leads chemists to the concepts of electronegativity and polarizability, and thus to the classification of polar and non-polar bonds. In addition, the intermolecular interactions are normally viewed as physical phenomena without direct correlation to the chemical bond in any simplistic model.

Morse, Lennard-Jones, and Kratzer Potentials: A Canonical Perspective with Applications.

Canonical approaches are applied to classic Morse, Lennard-Jones, and Kratzer potentials. Using the canonical transformation generated for the Morse potential as a reference, inverse transformations allow the accurate generation of the Born-Oppenheimer potential for the H ion, neutral covalently bound H, van der Waals bound Ar, and the hydrogen bonded one-dimensional dissociative coordinate in a water dimer. Similar transformations are also generated using the Lennard-Jones and Kratzer potentials as references.

Canonical Force Distributions in Pairwise Interatomic Interactions from the Perspective of the Hellmann-Feynman Theorem.

Force-based canonical approaches have recently given a unified but different viewpoint on the nature of bonding in pairwise interatomic interactions. Differing molecular categories (covalent, ionic, van der Waals, hydrogen, and halogen bonding) of representative interatomic interactions with binding energies ranging from 1.01 to 1072.

Canonical Approaches to Applications of the Virial Theorem.

Canonical approaches are applied for investigation of the extraordinarily accurate electronic ground state potentials of H2(+), H2, HeH(+), and LiH using the virial theorem. These approaches will be dependent on previous investigations involving the canonical nature of E(R), the Born-Oppenheimer potential, and F(R), the associated force of E(R), that have been demonstrated to be individually canonical to high accuracy in the case of the systems investigated. Now, the canonical nature of the remaining functions in the virial theorem [the electronic kinetic energy T(R), the electrostatic potential energy V(R), and the function W(R) = RF(R)] are investigated and applied to H2, HeH(+), and LiH with H2(+) chosen as reference.

Canonical Potentials and Spectra within the Born-Oppenheimer Approximation.

A generalized formulation of canonical transformations and spectra are used to investigate the concept of a canonical potential strictly within the Born-Oppenheimer approximation. Data for the most accurate available ground electronic state pairwise intermolecular potentials in H2, HD, D2, HeH(+), and LiH are used to rigorously evaluate such transformations. The corresponding potentials are generated explicitly using parameters calculated with algebraic functions from that of the single canonical potential of the simplest molecule, H2(+).

A general transformation to canonical form for potentials in pairwise interatomic interactions.

A generalized formulation of explicit force-based transformations is introduced to investigate the concept of a canonical potential in both fundamental chemical and intermolecular bonding. Different classes of representative ground electronic state pairwise interatomic interactions are referenced to a chosen canonical potential illustrating application of such transformations. Specifically, accurately determined potentials of the diatomic molecules H2, H2(+), HF, LiH, argon dimer, and one-dimensional dissociative coordinates in Ar-HBr, OC-HF, and OC-Cl2 are investigated throughout their bound potentials.

Pressure effects on the relaxation of an excited nitromethane molecule in an argon bath.

Classical molecular dynamics simulations were performed to study the relaxation of nitromethane in an Ar bath (of 1000 atoms) at 300 K and pressures 10, 50, 75, 100, 125, 150, 300, and 400 atm. The molecule was instantaneously excited by statistically distributing 50 kcal/mol among the internal degrees of freedom. At each pressure, 1000 trajectories were integrated for 1000 ps, except for 10 atm, for which the integration time was 5000 ps.

The Badger-Bauer rule revisited: correlation of proper blue frequency shifts in the OC hydrogen acceptor with morphed hydrogen bond dissociation energies in OC-HX (X = F, Cl, Br, I, CN, CCH).

Potential morphing has been applied to the investigation of proper blue frequency shifts, Δν0 in CO, the hydrogen acceptor complexing in the hydrogen bonded series OC-HX (X= F, Cl, Br, I, CN, CCH). Linear correlations of morphed hydrogen bonded ground dissociation energies D0 with experimentally determined Δν0 free from matrix and solvent effects demonstrate consistency with original tenets of the Badger-Bauer rule (J. Chem.

Post-shock relaxation in crystalline nitromethane.

Molecular dynamics simulations of shocked (100)-oriented crystalline nitromethane were carried out to determine the rates of relaxation behind the shock wave. The forces were described by the fully flexible non-reactive Sorescu-Rice-Thompson force field [D. C.

A classical trajectory study of the dissociation and isomerization of C2H5.

Motivated by photodissociation experiments in which non-RRKM nanosecond lifetimes of the ethyl radical were reported, we have performed a classical trajectory study of the dissociation and isomerization of C2H5 over the energy range 100-150 kcal/mol. We used a customized version of the AIREBO semiempirical potential (Stuart, S. J.

CMM-RS potential for characterization of the properties of the halogen-bonded OC-Cl2 complex, and a comparison with hydrogen-bonded OC-HCl.

Transitions associated with the vibrations ν₁, ν₁ + ν(b)¹, ν₁ + ν₅¹, and ν₁ + ν₅¹ - ν₅¹ of the complex OC···Cl₂ have been rovibrationally analyzed for several isotopologues involving isotopic substitutions in Cl₂. Spectra were recorded using a recently constructed near-infrared (4.34 to 4.

A ground state morphed intermolecular potential for the hydrogen bonded and van der Waals isomers in OC:HI and a prediction of an anomalous deuterium isotope effect.

An extended analysis of the noncovalent interaction OC:HI is reported using microwave and infrared supersonic jet spectroscopic techniques. All available spectroscopic data then provide the basis for generating an accurately determined vibrationally complete semiempirical intermolecular potential function using a four-dimensional potential coordinate morphing methodology. These results are consistent with the existence of four bound isomers: OC-HI, OC-IH, CO-HI, and CO-IH.

A four-dimensional compound-model morphed potential for the OC:HBr complex.

A parameterized compound-model morphed intermolecular potential energy surface has been generated for the dimer OC:HBr. This morphed potential is determined by fitting experimentally available gas phase spectroscopic data and found to have a global minimum with a well depth of 564(5) cm(-1) and linear (16)O(12)C-H(79)Br geometry having center of mass to center of mass distance R = 4.525(7) A.

Microwave-based structure and four-dimensional morphed intermolecular potential for HI-CO(2).

(Microwave spectra of the four isotopologue/isotopomers, HI-(12)C(16)O(2), HI-(12)C(18)O(2), HI-(12)C(18)O(16)O, and HI-(12)C(16)O(18)O, have been recorded using pulsed-nozzle Fourier transform microwave spectroscopy. In the last two isotopomers, the heavy oxygen atom tilted toward and away from the HI moiety, respectively. Only b-type Ka = 1 <-- 0 transitions were observed.