Search

In the supramolecular complex H2@C60, the lightest of molecules, H2, is encapsulated inside the most highly symmetric molecule C60. The elegance and apparent simplicity of H2@C60 conceal highly intricate quantum dynamics of the coupled translational and rotational motions of the guest molecule in a nearly spherical nanoscale cavity, which embodies some of the most fundamental concepts of quantum mechanics. Here we present the first rigorous and highly accurate quantum calculations of the inelastic neutron scattering (INS) spectra of this prototypical endohedral fullerene complex and their temperature dependence. The calculations enable complete assignment of the recently reported experimental INS spectra of H2@C60 measured at several temperatures. We also derive a new and unexpected selection rule for the INS spectroscopy of H2 in a near-spherical confinement, which explains why the INS transitions between certain translation-rotation eigenstates of H2 in C60 have zero intensity and do not appear in the spectra. [ABSTRACT FROM AUTHOR]

We report rigorous quantum five-dimensional (5D) calculations of the coupled translation-rotation (TR) energy levels and wave functions of an H2 molecule, in the ground (ν = 0) and vibrationally excited (ν = 1) states, confined inside the octahedral interstitial site of solid C60 with S6 symmetry. Translational and rotational excitations of H2 in this nanocavity have been measured by the inelastic neutron scattering (INS) and infrared (IR) spectroscopy, enabling direct comparison between theory and experiment. A pairwise additive 5D intermolecular potential energy surface (PES) was employed in the calculations. The quantum calculations cover the range of energies and types of translational and rotational excitations of the guest molecule which go substantially beyond those considered in the earlier theoretical investigations of this system, revealing new information about the TR energy level structure. The computed j = 1 and j = 2 rotational levels and their splittings, as well as the translational fundamental, are in semi-quantitative agreement with the available INS and IR data, indicating the need for a more accurate intermolecular PES. Our calculations reveal a strong dependence of the TR energy levels, in particular their splittings, on the setting angle which defines the orientation of the C60 molecules relative to their local threefold axes. [ABSTRACT FROM AUTHOR]

A two-dimensional (rigid monomer) intermolecular potential energy surface (PES) of the He–HCl complex has been obtained from ab initio calculations utilizing the symmetry-adapted perturbation theory (SAPT) and an spdfg basis set including midbond functions. The bond length in HCl was chosen to be equal to the expectation value in the ground vibrational state of isolated HCl. The rigid-monomer potential should be a very good approximation to the complete (three-dimensional) potential for H–Cl distances corresponding to the lowest vibrational levels of the monomer since the He–HCl interaction energy was found to be only weakly dependent on the HCl bond length in this region, at least as compared to systems such as Ar–HF. The calculated points were fitted using an analytic function with ab initio computed asymptotic coefficients. As expected, the complex is loosely bound, with the dispersion energy providing the majority of the attraction. Our SAPT PES agrees with the semiempirical PES of Willey et al. [J. Chem. Phys. 96, 898 (1992)], in finding that, atypically for rare gas–hydrogen halide complexes including the lighter halide atoms, the global minimum is on the Cl side (with intermonomer separation 3.35 Å and depth of 32.8 cm-1), rather than on the H side, where there is only a local minimum (3.85 Å, 30.8 cm-1). The ordering of the minima was confirmed by single-point calculations in larger basis sets and complete basis set extrapolations, and also using higher levels of theory. We show that the opposite findings in the recent calculations of Zhang and Shi [J. Mol. Struct: THEOCHEM 589, 89 (2002)] are due to the lack of midbond functions in their basis set. Despite the closeness in depth of the two linear minima, the existence of a relatively high barrier between them invalidates the assumption of isotropy, a feature of some literature potentials. The trends concerning the locations of minima within the family of rare gas–hydrogen halide complexes are rationalized in terms of the physical components of the intermolecular forces and related to monomer properties. The accuracy of the SAPT PES was tested by performing calculations of rovibrational levels. The transition frequencies obtained were found to be in excellent agreement (to within 0.02 cm-1) with the measurements of Lovejoy and Nesbitt [J. Chem. Phys. 93, 5387 (1990)]. The SAPT PES predicts a dissociation energy for the complex of 7.74 cm-1 which is probably more accurate than the experimental value of 10.1±1.2 cm-1. Our analysis of the ground-state rovibrational wave function shows that the He–HCl configuration is favored over the He–ClH configuration despite the ordering of minima. This is due to the greater volume of the well in the former case. We have also determined positions and widths of three low-lying resonance states through scattering calculations. These predictions are expected to be more accurate than values derived from experiment.© 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

New low-lying isomeric structures of ArnHF clusters are reported for n=6–13. They were determined using simulated annealing and evolutionary programing, for pairwise additive intermolecular potential energy surfaces. New global minima were found for the clusters with n=7, 10, 11. The new lowest-energy structure of Ar7HF and several new local minima for n=6, 7 clusters have the HF bound on a threefold surface site, consistent with the recent spectroscopic data for ArnHF clusters in helium nanodroplets. A new type of low-energy local minima were determined for n=9–13 clusters. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The equilibrium and low-lying isomeric structures of Ar[sub n]OH (X²Π) clusters for n = 1 to 15 are investigated by simulated annealing calculations. Potential energy surfaces are obtained by a pairwise-additive approach, taking into account the open-shell nature of OH X²Π and including spin-orbit coupling. It is found that the spin-orbit coupling suppresses the Jahn-Teller effect, and many of the clusters have high-symmetry structures (C[sub nv] with n > 2) which would be forbidden in the absence of spin-orbit coupling. The structures are generally similar to those previously found for the closed-shell systems Ar[sub n]HF and Ar[sub n]HCl, but different from those for the open-shell systems Ar[sub n]NO and Ar[sub n]CH. This is because Ar-OH (X²Π), like Ar-HF and Ar-HCl but unlike Ar-NO and Ar-CH, has a near-linear equilibrium structure. Ar[sub n]OH clusters for n up to 6 have all Ar atoms in a single shell around OH. In the clusters with n = 7 to 9, OH is under a pentagonal pyramid formed by six Ar atoms, while the others bind to its exterior, away from OH. For n = 10 to 12, the minimum-energy structures have OH inside an Ar[sub n] cage, which is essentially icosahedral for n = 12 but has vacancies for n = 10 and 11. For n > 12, the extra Ar atoms begin to form a second solvation shell. The global minimum of Ar[sub n],OH may be constructed from the minimum-energy structure of Ar[sub n + 1] by replacing one Ar atom with OH. [ABSTRACT FROM AUTHOR]

This paper presents a theoretical study of the bound states of the open-shell OH radical in its ground electronic state (X[sup 2]H) interacting with n Ar atoms, for n from 4 to 12. After freezing the geometry of the Ar[sub n] cage or subunit at the equilibrium structure (preceding paper), we carry out nonadiabatic five-dimensional quantum dynamics calculations on two coupled potential energy surfaces, using an extension of the method previously applied to closed-shell Ar[sub n]HF clusters [J. Chem. Phys. 103, 1829 (1995)]. The method is based on a discrete variable representation (DVR) for the translational motion of OH relative to Ar[sub n], combined with a finite basis representation of the OH hindered rotation and electronic structure, including spin-orbit effects. The pattern of OH hindered rotor levels in clusters is similar to that in Ar-OH itself, though extended over three to four times the energy range for n = 4 to 9. Ar[sub 12]OH has a nearly spherical shell of Ar atoms around the OH, so the anisotropic splitting is very small. For n = 10 and 11, the anisotropy may be viewed as arising from holes in an otherwise spherical shell, and the resulting patterns of hindered rotor levels are inverted versions of those for Ar2OH and Ar-OH. [ABSTRACT FROM AUTHOR]

The HF vibrational frequency shifts for ArnHF van der Waals (vdW) clusters with n=4–14 are predicted to be strongly isomer-specific, providing distinct spectroscopic signatures for different cluster isomers. This represents an extension of our recent studies of the size dependence of the vibrational frequency shift for ArnHF clusters [J. Chem. Phys. 101, 6359, 10 181 (1994)]. The HF vibrational frequency shifts calculated for the two or three lowest-energy isomers of each cluster size considered differ by at least a couple of wave numbers. Their relative magnitudes directly reflect the number of Ar atoms that each ArnHF isomer has in the first solvation shell around HF. The calculations are performed on pairwise additive intermolecular potential energy surfaces constructed from spectroscopically accurate Ar–Ar and anisotropic Ar–HF potentials. In the frequency shift calculations, the Arn subunit is treated as rigid, frozen in the geometry of one of the global or local ArnHF minima found previously by simulated annealing [J. Chem. Phys. 100, 7166 (1994)]. The 5D coupled intermolecular vibrational levels of what is now effectively a floppy Arn–HF dimer, are calculated highly accurately by the quantum 5D bound state methodology which is described in detail. The 5D vdW vibrational zero-point energy of the ArnHF cluster affects significantly the energy gap between various isomers. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Theoretical study of the influence of excited intermolecular vibrations on the total and partial decay widths of HF dimer is reported. Vibrational predissociation (VP) lifetimes and rotational state distributions of HF fragments were calculated for various quasibound states of (HF)2, corresponding to combinations of the intermolecular stretching (ν4) and bending (ν5) vibrations with the ‘‘free’’ (ν1) and ‘‘bonded’’ (ν2) HF stretch fundamentals, for total angular momentum J=1, K=0. The calculations were performed on an ab initio six-dimensional potential energy surface of Quack and Suhm, using a quantum four-dimensional golden rule methodology. The VP lifetimes and product rotational distributions exhibit pronounced dependence on the type of the initially excited intermolecular vibration of HF dimer. The energy deposited in the ν4 intermolecular stretch evolves into the translational energy of the fragments. Excitation of the ν5 intermolecular bending vibration, combined with the ν1 fundamental, is transferred to the product rotational energy. This is in good agreement with the experimental results of Bohac and Miller. We also found that in conjunction with the ν2 fundamental, most of the ν5 bending vibrational energy emerges in the translational energy of the products. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Size evolution of the equilibrium structures of ArnH2O van der Waals clusters with n=1–14 has been investigated. Pairwise additive intermolecular potential energy surfaces (IPESs) for ArnH2O clusters were constructed from the spectroscopically accurate Ar–Ar and anisotropic 3D Ar–H2O potentials. For each cluster size considered, we determined the global minimum of the respective IPES and several other lowest-lying ArnH2O isomeric structures. This was accomplished by using simulated annealing followed by a direct minimization scheme. The minimum-energy structures of all ArnH2O clusters considered in this work are fully solvated; up to n=12, the Ar atoms fill a monolayer around H2O. For n=12, the optimal Ar12H2O structure has the Ar atoms arranged in a highly symmetrical icosahedron, with H2O in its center. The icosahedral Ar12H2O structure is exceptionally stable; the energy gap separating it from the next higher n=12 isomer (289.55 cm-1) exceeds that for any other cluster in this size range. The observed preference for solvated ArnH2O structures was carefully analyzed in terms of the relative energetic contributions from Ar–Ar and Ar–H2O interactions. For n≤9, the monolayer, cagelike geometries are favored primarily by providing optimal Ar–H2O interactions, significantly larger than for alternative ArnH2O structures. For n>=9, the solvated ArnH2O isomers offer the best Ar–Ar packing, in addition to the strongest total Ar–H2O interactions. A detailed comparison was made with the minimum-energy structures of ArnHF clusters, determined by us recently [J. Chem. Phys. 100, 7166 (1994)], revealing interesting differences in the growth patterns of the optimal cluster structures. [ABSTRACT FROM AUTHOR]

Detailed results of the quantum 3D calculation of the intermolecular vibrational levels of the endohedral fullerene complex Ne[ATOTHER]@xa[/ATOTHER]C70, for the total angular momentum J=0, are presented. They elucidate, for the first time, the nature of the endohedral vibrations of an atom inside a strongly nonspherical fullerene. The calculations were performed using our recently developed method for accurate highly excited 3D intermolecular vibrational states of atom–large molecule complexes [J. Chem. Phys. 98, 7165 (1993)]. The treatment of the coupled endohedral vibrations of Ne[ATOTHER]@xa[/ATOTHER]C70 involves no dynamical approximations, apart from taking the fullerene to be rigid, producing eigenstates which are essentially exact for the intermolecular potential energy surface (PES) employed. The 3D endohedral PES for Ne[ATOTHER]@xa[/ATOTHER]C70, modeled as a sum of atom–atom Lennard-Jones pair potentials, is anharmonic, especially in the direction of the long (z) axis of C70. The endohedral vibrational energy level structure of Ne[ATOTHER]@xa[/ATOTHER]C70 which emerged from our calculations is surprisingly simple. The coupling between the vibrational mode parallel to the long (z) axis of C70 and the modes perpendicular to it, is weak. The two endohedral modes perpendicular to the (z) axis represent an exemplary case of a 2D isotropic, anharmonic oscillator. The fundamental frequencies for the parallel and perpendicular endohedral mode of Ne[ATOTHER]@xa[/ATOTHER]C70, calculated using the present PES, are 9.83 and 54.49 cm-1, respectively. The wave functions of all endohedral vibrational states of Ne[ATOTHER]@xa[/ATOTHER]C70 up to at least 240 cm-1 above the ground state, considered in this work, have exceptionally regular nodal patterns, allowing complete and unambiguous quantum number assignment. [ABSTRACT FROM AUTHOR]

This paper presents a theoretical study of the size evolution of equilibrium structures and approximate HF vibrational red shifts for ArnHF van der Waals clusters, with n=1–14. Pairwise additive ArnHF intermolecular potential energy surfaces were constructed from spectroscopically accurate Ar–Ar and anisotropic Ar–HF potentials. The latter depend on vibrational excitation of the HF monomer. The global and energetically close-lying local minima of ArnHF, n=1–14, for HF v=0 and v=1, were determined using simulated annealing followed by a direct minimization scheme. For ArnHF clusters with n≤8, the lowest-energy structure always has HF bound to the surface of the Arn subunit. In contrast, for n≥9, the global minimum of ArnHF corresponds to HF inside a cage. Ar12HF has the minimum-energy configuration of an HF-centered icosahedron, which appears to be unusually stable. Size dependence of the HF vibrational red shift in ArnHF (n=1–14) clusters was investigated by means of a simple approximation, where the red shift was represented by the energy difference between the global minima of a cluster obtained for HF v=0 and v=1, respectively. The approximation reproduced rather accurately the experimentally determined variation of the ArnHF red shift with the number of Ar atoms, for n=1–4, although it overestimated their magnitude. For larger ArnHF clusters, 4

A combined experimental and theoretical study of the intermolecular vibrations of 2,3-dimethylnaphthalene·Ar (2,3-DMN·Ar), for the first excited electronic state (S1), is reported. Methyl groups at C2 and C3 positions of naphthalene lower the symmetry of the complex, so that transitions involving excitation of the intermolecular long-axis in-plane x mode become allowed in electronic spectra, in addition to the out-of-plane z mode. Two-color resonant two-photon ionization (2C-R2PI) spectrum of the van der Waals (vdW)-mode region (000+70 cm-1) of 2,3-DMN·Ar exhibits six bands to the high-frequency side of the electronic origin 000, which arise from excitation of low-frequency intermolecular vibrations of the complex in the S1 state. Accurate quantum three-dimensional (3D) calculations of vdW vibrational (J=0) levels of S1 2,3-DMN·Ar have been performed, using a recently developed quantum method based on the 3D discrete variable representation. Since no approximation is made in the treatment of coupled, very anharmonic vdW vibrations, the calculated eigenstates are essentially exact for the intermolecular potential energy surface (PES) employed, thus enabling direct comparison between theory and experiment. The intermolecular PES was modeled as a sum of atom–atom Lennard-Jones (LJ) pair potentials. Some of the initial LJ parameters were modified until very good agreement was achieved between the calculated and measured vdW frequencies of S1 2,3-DMN·Ar. This allowed assignment of the vdW bands to the blue side of 000, and resulted in an improved intermolecular PES of the complex. In addition, the quantum 3D calculations provided a quantitative description of the vdW vibrational level structure and floppiness of S1 2,3-DMN·Ar up to ∼60–70 cm-1 above the ground vdW state. The wave functions of all vdW states below ∼49 cm-1, relative to the ground state, are sufficiently regular to allow assignment... [ABSTRACT FROM AUTHOR]

We present an accurate and efficient method for calculating highly excited 3D van der Waals (vdW) vibrational states of structurally nonrigid M·R complexes between an atom R and a large, arbitrarily shaped molecule M. Our method combines the atom–molecule Hamiltonian of Brocks and van Koeven, in which Cartesian components of the vector connecting R and the center of mass of M are used as internal coordinates, with the 3D discrete variable representation (DVR) of all three intermolecular large amplitude degrees of freedom. Our 3D DVR method is aimed at highly anisotropic M·R complexes, in which the size of the molecule is typically larger than the average atom–molecule distance. The symmetry of the complex (if any) is exploited by constructing symmetry adapted 3D DVRs which transform under the irreducible representations of the symmetry group, and bring the Hamiltonian matrix to a block diagonal form. The 3D DVR is particularly well suited for description of excited and strongly coupled, delocalized vdW states, and internal motions on very anharmonic intermolecular potentials with multiple minima. We use this method to calculate vdW vibrational energy levels and wave functions of a floppy complex naphthalene·Ar. The lower-lying vdW states are assigned by inspection of the wave function plots. [ABSTRACT FROM AUTHOR]

We report a combined experimental and theoretical study of the van der Waals isomers and intermolecular vibrations of the 2,3-dimethylnaphthalene·Ne complex in the S1 electronic state. The two-color resonant two-photon ionization spectrum exhibits eight bands within ≊40 cm-1 of the electronic origin. Theoretical considerations in combination with hole-burning spectroscopic measurements show that the transition closest to the electronic origin (at 000+5 cm-1) arises from an isomer which is different from that responsible for the other seven bands in the spectrum. The latter involve excitations of the intermolecular vibrations of the main isomer of 2,3-dimethylnaphthalene·Ne. Accurate three-dimensional quantum calculations of the van der Waals vibrational levels of the complex were performed using a discrete variable representation method. Combination of theory and experiment led to a complete assignment as well as to a quantitative theoretical reproduction of the experimental intermolecular vibrational level structure, and a parametrization of the intermolecular potential energy surface, modeled as sum of atom–atom Lennard-Jones pair potentials. This potential surface exhibits a global minimum above (and below) the aromatic ring plane of 2,3-dimethylnaphthalene and a shallower local minimum at C2v geometry, on the C2 axis of the molecule, adjacent to the two methyl groups. The main and minor isomers identified experimentally are associated with the global and the local minimum, respectively. The quantum calculations were extended to ≊1000 van der Waals vibrational states, i.e., to energies up to 78% of D0. These include levels localized either in the global or local minima, as well as highly excited vibrational states delocalized over all three potential minima, providing comprehensive insight into the quantum dynamics of the high-lying van der Waals states of an atom–large aromatic molecule complex. © 1995 American... [ABSTRACT FROM AUTHOR]

We report a detailed experimental and theoretical study of the intermolecular vibrational levels of the 1,2-dimethylnaphthalene·Ar van der Waals complex in the S1 electronic state. Due to the low symmetry of the aromatic molecular substrate, excitations in all three van der Waals modes (two in-plane, one out-of-plane) are allowed in the electronic spectrum, leading to the most complete data set of intermolecular vibrational transitions measured so far for an atom-large molecule complex. Two-color resonant two-photon ionization spectra reveal twelve bands within ≊95 cm-1 of the electronic origin. Accurate quantum three-dimensional calculations of the van der Waals vibrational levels were performed, using a method based on the 3D discrete variable representation. Combination of theory and experiment allowed a complete and quantitative interpretation of the level structure, as well as an accurate parametrization of the intermolecular potential energy surface (PES), modeled as sum of atom–atom Lennard-Jones pair potentials. The parametrization was partly transferable from other aromatic molecules, but methyl group parameters had to be adapted. Quantum number assignments of the vibrational states were possible for the low-lying levels, but difficult or impossible for states at higher energies, due to strong mode coupling, mainly between the two in-plane modes. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Detailed results of the converged full-dimensional 6D quantum calculations of the vibrational levels of (HF)2, (DF)2, and HFDF, for total angular momentum J=0, are presented. The ab initio 6D potential energy surface by Quack and Suhm was employed. This study provides a comprehensive description of the bound state properties of the HF dimer and its isotopomers, including their dissociation energies, frequencies of the intermolecular vibrations, tunneling splittings, and extent of wave function delocalization. Quantum number assignment of the calculated eigenstates by plotting different cuts through the wave functions worked rather well for (HF)2, but proved to be much harder for (DF)2 and HFDF, indicating stronger vibrational mode mixing in these species. The ground-state tunneling splitting for the HF dimer from our exact 6D calculations, 0.44 cm-1, is very close to that from a previous 4D rigid-rotor calculation, 0.48 cm-1 [J. Chem. Phys. 99, 6624 (1993)]. This is in disagreement with the result of a recent 6D bound state calculation for (HF)2 by Necoechea and Truhlar, which gave a ground-state tunneling splitting a factor of 3.7 times larger than the 4D result. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A combined experimental and theoretical study of the intermolecular vibrations of the o-xylene·Ar van der Waals complex is reported for both the S0 and S1 electronic states. Two-color resonant two-photon ionization and fluorescence emission spectra of the vdW mode region of supersonic jet-cooled o-xylene·Ar exhibit five bands within 70 cm-1 of the electronic origin, which arise from low-frequency large-amplitude intermolecular vibrations. Accurate quantum 3D calculations of vdW vibrational levels were performed, based on the 3D discrete variable representation. Apart from the restriction to the J=0 state the calculated eigenstates are exact for the intermolecular potential energy surface (PES) employed. The PES is represented as a sum of Lennard-Jones (LJ) pair potentials, and the direct comparison between theory and experiment enabled calibration of the LJ parameters. Very good agreement was achieved for both the S0 and S1 states of o-xylene·Ar. The quantum 3D calculations provide a quantitative description of the vdW level structure up to ≊70 cm-1 above the vdW ground state. The low-energy eigenfunctions have nodal patterns analogous to the 2,3-dimethylnaphthalene·Ar complex. However, in the energy range 40–60 cm-1 the vdW mode eigenfunctions change over to 2D radial-oscillator-type wave functions, similar to those of benzene·Ar, but switch back to Cartesian type above 60 cm-1. The S1 state vdW levels of 2,3-dimethylnaphthalene [M. Mandziuk, Z. Bacˇic, T. Droz, and S. Leutwyler, J. Chem. Phys. 100, 52 (1994)] were recalculated with the present parameters, and the agreement between experimental and calculated frequencies is improved. [ABSTRACT FROM AUTHOR]

We investigate the cage effect in the ultraviolet (UV) photodissociation of the Ar...HCl van der Waals complex, especially the possibility of resonance structures caused by trapping of the hydrogen atom between its heavy partners as recently highlighted by Garcia-Vela and Gerber [J. Chem. Phys. 98, 427 (1993)]. The dynamics is described by solving the time-dependent Schrödinger equation employing the standard Jacobi coordinates which are routinely used for triatomic systems. Due to the large size of the required grid, exact three-dimensional (3D) wave packet calculations are extremely time consuming and could be followed up to 20 fs only. This time is sufficient for calculating the absorption spectrum, but too short for determining the final kinetic energy distributions of the fragment atoms. Therefore, the photodissociation dynamics is mainly treated in a vibrationally sudden approximation, in which the dynamical calculations are performed for a range of fixed ArCl bond distances, and the results averaged over this bond length. 3D classical trajectory calculations show that the energy transfer out of the dissociative HCl mode is very weak (∼5% of the total energy), supporting the application of the sudden approximation. In this approximation, both the absorption spectrum and the kinetic energy distribution associated with the dissociating HCl motion exhibit very weak diffuse structures (resonances) which, following the work of Garcia-Vela and Gerber, can be assigned to the transient vibrational motion of hydrogen between Ar and Cl. However, in our calculations these structures are much less pronounced than in the work of Garcia-Vela and Gerber. The very small amplitudes of the resonance features indicate that trapping in the dissociation of HCl in Ar...HCl is marginal, and much less important than suggested by the previous studies of Garcia-Vela et al. Furthermore, in contrast to the work reported by Garcia-Vela et al., we do not find any evidence... [ABSTRACT FROM AUTHOR]

Calculations of the total and partial decay widths are presented for the vibrational predissociation of D2HF. The calculation is done for the total angular momentum J=0 of the molecule and for the dissociation process D2HF(v=1)→D2(v=1)+HF(v=0), which is the dominant decaying channel. A time-dependent wave packet approach in the golden rule approximation is employed in the numerical calculation for the decay widths. Our computed total and partial decay widths are in good agreement with those from a time-independent scattering calculation. The time-dependent golden rule wave packet method, which does not solve coupled channel scattering equations, offers an efficient alternative to the time-independent scattering method for computing the decay widths in vibrational predissociation for relatively large molecules. The total time of propagation required in the golden rule wave packet calculation is determined by the duration time of the final state interaction between the fragments on the vibrationally deexcited adiabatic potential surface. This interpretation clearly explains the fact that only a short time is needed in our wave packet propagation, regardless of how long the lifetime of the predissociating state may be. [ABSTRACT FROM AUTHOR]

Quantum 5D bound state calculations for the fully solvated Ar12HF cluster, with the Ar atoms frozen at their icosahedral equilibrium geometry, gave the HF vibrational redshift of 42.46 cm-1. This value is equal to that measured for HF in an Ar matrix, 42.4 cm-1. [ABSTRACT FROM AUTHOR]

We have performed high-resolution inelastic neutron scattering (INS) measurements on binary hydrogen clathrate hydrates exhibiting the hexagonal structure (sH). Two samples, differing only in the ortho/para fraction of hydrogen, were prepared using heavy water and methyl tert-butyl ether as the promoter in its perdeuterated form. The INS spectrum of the translation-rotation (TR) excitations of the guest H2 molecule was obtained by subtracting the very weak signal due to the D2O lattice modes. By means of a subtraction procedure, it has been possible to obtain separately the spectra of caged p-H2 and o-H2. sH clathrates are comprised of three distinct types of cages, two of which, differing in shape and size, are each occupied by one H2 molecule only. Both contribute to the measured INS spectrum which is, therefore, rather complex and challenging to assign unambiguously. To assist with the interpretation, the INS spectra are calculated accurately utilizing the quantum methodology which incorporates the coupled five-dimensional TR energy levels and wave functions of the H2 molecule confined in each type of nanocage. The computed INS spectra are highly realistic and reflect the complexity of the coupled TR dynamics of the guest H2 in the anisotropic confining environment. The simulated INS spectra of p-H2 and o-H2 in the small and medium cages are compared with the experimental data, and are indispensable for their interpretation. [ABSTRACT FROM AUTHOR]

We report rigorous quantum five-dimensional (5D) calculations of the coupled translation-rotation (T-R) eigenstates of a H2 molecule adsorbed in metal organic framework-5 (MOF-5), a prototypical nanoporous material, which was treated as rigid. The anisotropic interactions between H2 and MOF-5 were represented by the analytical 5D intermolecular potential energy surface (PES) used previously in the simulations of the thermodynamics of hydrogen sorption in this system [Belof et al., J. Phys. Chem. C 113, 9316 (2009)]. The global and local minima on this 5D PES correspond to all of the known binding sites of H2 in MOF-5, three of which, α-, β-, and γ-sites are located on the inorganic cluster node of the framework, while two of them, the δ- and [variant_greek_epsilon]-sites, are on the phenylene link. In addition, 2D rotational PESs were calculated ab initio for each of these binding sites, keeping the center of mass of H2 fixed at the respective equilibrium geometries; purely rotational energy levels of H2 on these 2D PESs were computed by means of quantum 2D calculations. On the 5D PES, the three adjacent γ-sites lie just 1.1 meV above the minimum-energy α-site, and are separated from it by a very low barrier. These features allow extensive wave function delocalization of even the lowest translationally excited T-R eigenstates over the α- and γ-sites, presenting significant challenges for both the quantum bound-state calculations and the analysis of the results. Detailed comparison is made with the available experimental data. [ABSTRACT FROM AUTHOR]