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  • 1
    Electronic Resource
    Electronic Resource
    Six-dimensional quantum calculations of vibration-rotation-tunneling levels of ν1 and ν2 HCl-stretching excited (HCl)2 (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 4804-4816 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Results of the first full-dimensional (6D) quantum calculations of the vibrational levels of the ν1 and ν2 HCl-stretch excited (HCl)2, for total angular momentum J=0, are presented. Three 6D potential energy surfaces (PESs) were employed. Two widely used PESs, the ab initio PES of Bunker and co-workers and the semiempirical PES by Elrod and Saykally, are found to give negligible tunneling splittings (≤5×10−2 cm−1) for the vibrational eigenstates of the ν1/ν2 excited (HCl)2, in sharp disagreement with the experimental tunneling splittings in the ν1 and ν2 fundamentals, −3.32 and 3.18 cm−1. In an effort to overcome this problem, a 6D electrostatic interaction potential is constructed and added to the ES1 PES; the resulting 6D PES is denoted ES1-EL. Quantum 6D calculations on the ES1-EL PES yield greatly improved tunneling splittings for ν1 (−2.31 cm−1) and ν2 (2.45 cm−1), which are 70% and 77%, respectively, of the corresponding experimental values. The ν1 and ν2 fundamental HCl-stretching frequencies calculated on the ES1-EL PES are only 5.9 cm−1 lower and 2.9 cm−1 higher, respectively, than their experimental counterparts. In addition, the quantum 6D calculations on the ES1-EL PES provide a comprehensive characterization of the ν1/ν2 supported vibrational eigenstates of (HCl)2, including their energies, assignments, and tunneling splittings. The vibration-rotation-tunneling dynamics of (HCl)2 in the ν1 and ν2 excited states which emerged from our calculations differs substantially from that observed for the HF-stretch excited (HF)2. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475891
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  • 2
    Electronic Resource
    Electronic Resource
    Exact six-dimensional quantum calculations of the rovibrational levels of (HCl)2 (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 2158-2170 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Results of comprehensive full-dimensional (6D) quantum calculations of the rovibrational levels of (HCl)2, for total angular momentum J=0,1 are presented. The calculations employed two 6D potential energy surfaces (PES)—the ab initio PES of Bunker and co-workers, and the semiempirical PES of Elrod and Saykally. This 6D study provides the first rigorous, approximation-free description of the bound state properties of (HCl)2, including the dissociation energy, tunneling splittings and their J, K dependence, frequencies of intermolecular vibrations and associated J=0→1 spacings, and quantum number assignments of the 6D eigenstates. Detailed comparison with 4D bound state calculations (for fixed HCl bond length) was made in order to assess the importance of including the intramolecular vibrations of the two HCl subunits for accurate calculation of various spectroscopic properties of (HCl)2. Comparison of the 6D results with experimental data, while confirming that the ES1 PES is substantially more accurate than the ab initio PES, shows that there is room for further refinements, preferably using 6D bound state calculations. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473139
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  • 3
    Electronic Resource
    Electronic Resource
    Six-dimensional quantum treatment of the vibrations of diatomic adsorbates on solid surfaces: CO on Cu(100) (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 11164-11176 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Computational methodology for exact quantum 6D calculations of the vibrational eigenstates, energy levels, and wave functions of a diatomic molecule adsorbed on a rigid corrugated surface is presented. It is intended for adsorbates executing coupled, strongly anharmonic large-amplitude vibrations. Surface nonrigidity is introduced in an approximate way, by means of a simplified surface-mass model. Using this methodology, we calculate the vibrational levels of CO/Cu(100) for all four isotopomers of CO, 12C16O, 13C16O, 12C18O, and 13C18O. The empirical potential by Tully and co-workers [J. C. Tully, M. Gomez, and M. Head-Gordon, J. Vac. Sci. Technol. A 11, 1914 (1993)] is employed. Our calculated fundamental frequencies of CO/Cu(100) vibrations are compared to those from earlier theoretical treatments on the same potential, as well as with the experimental frequencies and isotope frequency shifts. In addition to 6D calculations, we perform 5D (rigid CO) and 4D (fixed-site) quantum calculations, which provide information about the couplings among the vibrational modes of CO on Cu(100). Excited levels of the lowest-frequency in-plane (doubly degenerate) frustrated translation mode are analyzed and assigned. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480494
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  • 4
    Electronic Resource
    Electronic Resource
    Calculated and experimental rotational constants of (D2O)3: Effects of intermolecular torsional and symmetric stretching excitations (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 5331-5337 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Calculations of the torsional state dependence of A=B and C rotational constants of (D2O)3 are reported, for torsional energies up to 100 cm−1 above the ground state, extending our work on the rotational constants of all isotopomers of water trimer using ab initio four-dimensional torsional-stretching intermolecular potential-energy surface [D. Sabo et al., J. Phys. Chem. 110, 5745 (1999)]. Direct composition was made to the rotational constants measured by Viant et al. [J. Chem. Phys. 110, 4369 (1999)] for the same nine torsional levels of (D2O)3. In order to consistently reproduce the pronounced variations of the A=B and C rotational constants from one torsional eigenstate to the other, theory must take into account both the changes of rms torsional angles of the "free" O–D bonds and the changes in the oxygen–oxygen separation which accompany torsional excitation. The changes of C with torsional state, ΔC(n), are distinctly non-monotonic; they depend mainly on the rms (root-mean-square) torsional angle and to a lesser degree on the interoxygen distance. The changes of A=B with torsional state, ΔA(n)=ΔB(n), depend on both rms torsional angles and interoxygen distance, but with opposite signs, giving rise to an apparent monotonic decrease with n which is smaller than the changes due to either mechanism alone. The ΔA(n)=ΔB(n) and ΔC(n) changes from the (3+1)D torsional-stretching calculations are in good agreement with experiment up to n=5. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479792
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  • 5
    Electronic Resource
    Electronic Resource
    Four-dimensional model calculation of torsional levels of cyclic water tetramer (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 5404-5419 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Quantum four-dimensional model calculations of the coupled intermolecular torsional vibrations of the cyclic homodromic water tetramers (H2O)4 and (D2O)4 are presented, based on the analytical modEPEN4B potential energy surface [S. Graf and S. Leutwyler, J. Chem. Phys. 109, 5393 (1998), preceding paper] and a four-dimensional discrete variable representation approach. The lowest 50 torsional levels were calculated up to 420 and 500 cm−1 for (D2O)4 and (H2O)4, respectively. For both clusters, the torsional ground state is split by a synchronous O–H torsional inversion process, similar to inversion tunneling in ammonia, with calculated tunnel splittings of 21.8 and 0.000 12 MHz for (H2O)4 and (D2O)4, respectively. As for the cyclic water trimer and pentamer, the four torsional fundamentals of the tetramer lie above the torsional interconversion barriers, between 185–200 cm−1 for (D2O)4 and 229–242 cm−1 for (H2O)4, but also lie below the one-dimensional torsionally adiabatic barriers. The anharmonic fundamental frequencies lie both above and below the normal-mode frequencies, by up to 33%. Slightly above the fundamental torsional excitations, at 257–260 and 280–281 cm−1 for (H2O)4 and (D2O)4, respectively, lie four states corresponding to four versions of the {uudd} isomer, which form a pseudorotational manifold; the torsional interconversion occurs by a sequence of double O–H flips. Higher excited pseudorotational states are calculated up to a vibrational angular momentum of k=3. At (approximate)295 and (approximate)300 cm−1, a further group of eight states is found, corresponding to the eight permutationally equivalent versions of yet another isomer, the {uuud} structure. The four {uudd} and eight {uuud} states of (H2O)4 exhibit inverse isotope effects, and lie at lower energy than their (D2O)4 counterparts. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477159
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  • 6
    Electronic Resource
    Electronic Resource
    Calculated and experimental rotational constants of (H2O)3: Effects of intermolecular torsional and symmetric stretching excitations (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 10727-10729 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Calculations of the torsional state dependence of the A=B and C rotational constants of (H2O)3 are reported, for torsional excitations up to 144 cm−1 above the ground state, extending our work on the rotational constants of all isotopomers of water trimer using an ab initio four-dimensional torsional-stretching intermolecular potential energy surface [D. Sabo et al., J. Chem. Phys. 110, 5745 (1999)]. Direct comparison was made to the rotational constants of (H2O)3 recently measured and analyzed by Brown et al. [J. Chem. Phys. 111, in press (1999)], for the lowest five torsional levels n=0–5, with torsional energies up to 80 cm−1. The results of the (3+1)-dimensional torsional-stretching calculations are in excellent agreement with experiment. The rotational constants of the next higher torsional level, n=6, were calculated by the (3+1)-dimensional method. A comparison is made to the rotational constants calculated by a three-dimensional purely torsional model, which yields inferior results. In order to consistently reproduce the pronounced variations of the A=B and C rotational constants from one torsional eigenstate to the other, theory must take into account both the changes of rms torsional angles of the "free" O–H bonds and the changes in the oxygen–oxygen separation which accompany torsional excitation. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480427
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  • 7
    Electronic Resource
    Electronic Resource
    Rotational constants of all H/D substituted water trimers: Coupling of intermolecular torsional and symmetric stretching modes (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 5745-5757 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A four-dimensional (4D) intermolecular potential energy surface (IPES) for the water trimer was calculated in the subspace of the three torsional coordinates and the symmetric intermolecular stretch coordinate, employing high-level ab initio theory. Torsionally adiabatic potential energy curves for the intermolecular symmetric stretching vibration were constructed based on this IPES. They were used to calculate the symmetric stretch fundamentals and stretching-averaged interoxygen R(O(centered ellipsis)O) distances 〈RH〉 and 〈RD〉, for the n=0–6 torsional levels of (H2O)3 and (D2O)3. 〈RH〉 and 〈RD〉 increase with n up to n=5, and decrease for n=6. Torsionally averaged rotational constants A, B, and C of all 20 isotopomers of water trimer, for the torsional levels n=0, 5 and 6, were obtained by averaging the inverse inertia tensor over the 3D torsional wave functions. Two approaches were examined: (i) setting the interoxygen R(O(centered ellipsis)O) distance to a fixed value, independent of torsional excitation; (ii) effectively incorporating the vibrational averaging due to the intermolecular symmetric stretching mode by using the appropriate 〈RH〉 and 〈RD〉 values to define the R(O(centered ellipsis)O) distances for the isotopomers in the torsional state n. Both approaches yielded n=0, 5 rotational constants in good agreement with experiment. However, only approach (ii) reproduced the experimentally observed decrease in the rotational constants A and B upon 5←0 torsional excitation. Fixing the R(O(centered ellipsis)O) distances to RH and RD values obtained by fitting the 3D torsionally averaged rotational constants to the experimental values for (H2O)3 and (D2O)3, only marginally improved the agreement with experiment for other isotopomers. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478473
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  • 8
    Electronic Resource
    Electronic Resource
    Exact full-dimensional bound state calculations for (HF)2, (DF)2, and HFDF (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 2315-2325 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468719
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  • 9
    Electronic Resource
    Electronic Resource
    HF vibrational redshift for the icosahedral Ar12HF van der Waals cluster is the same as in an Ar matrix: Quantum five-dimensional bound state calculations (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 6359-6361 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468390
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  • 10
    Electronic Resource
    Electronic Resource
    ArnH2O (n=1–14) van der Waals clusters: Size evolution of equilibrium structures (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 8310-8320 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: 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(approximately-greater-than)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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468097
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