Molecular orbital study of some protonated bases

Bene, Janet E. Del; Frisch, Michael J.; Raghavachari, Krishnan; Pople, John A.

doi:10.1021/j100206a013

Cited by 119 publications

(48 citation statements)

References 11 publications

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“…A study of various interaction terms and basis set effects for neutral (NH3) 2 [28] has been described in the literature. A study of various interaction terms and basis set effects for neutral (NH3) 2 [28] has been described in the literature.…”

Section: Potential Energy Surface Of the Ammonia Dimer Cationmentioning

confidence: 99%

Proton transfer in ammonia cluster cations: molecular dynamics in a self consistent field

Greer

Ahlrichs

Hertel

1991

Z Phys D - Atoms, Molecules and Clusters

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A theoretical study of the energetics and intramolecular dynamics for ammonia cluster cations (NH3) + and (NH3) + is presented. The proton transfer mechanism after a vertical ionisation is followed in detail. Structural and energetic calculations are performed near the Hartree-Fock self consistent field (HF-SCF) limit; all open shell calculations are spin restricted (RHF). The calculations reconcile experimental results from thermochemical and photoionisation measurements: discrepancies in the energetics are shown to be due to the probing of different regions of the potential energy surface (PES). For the dynamics calculations, it is impractical to determine a large region of the multidimensional PES and then integrate Newton's equations. The calculations therefore incorporate a quantum mechanical determination of the electronic energy of the system after each time increment while nuclear degrees of freedom are handled classically. In this way, the classical reaction path across the Born-Oppenheimer surface is obtained.

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Section: Potential Energy Surface Of the Ammonia Dimer Cationmentioning

confidence: 99%

Proton transfer in ammonia cluster cations: molecular dynamics in a self consistent field

Greer

Ahlrichs

Hertel

1991

Z Phys D - Atoms, Molecules and Clusters

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“…The latter result suggests that the larger water complexes have cyclic structures, in agreement with early ab initio calculations. 2 Employing molecular beam electric resonance spectroscopy in the radio frequency and microwave regimes, Dyke and co-workers 3,4 obtained detailed structural information on the dimer.…”

Section: Introductionmentioning

confidence: 99%

Infrared spectroscopy of small size-selected water clusters

Huisken

Kaloudis

Kulcke

1996

The Journal of Chemical Physics

457

416

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Infrared molecular beam depletion and fragment spectroscopy has been employed to study the absorption behavior of small water clusters ͓͑H 2 O͒ n , nϭ2,3,4,5͔. The spectral region between 3300 and 3800 cm Ϫ1 was covered with an injection-seeded optical parametric oscillator. Size-specific information has been obtained by dispersing the cluster beam with a secondary helium beam and measuring the depletion as a function of the scattering angle. Three absorption bands could be assigned to the water dimer ͑H 2 O͒ 2 , with the bonded OH stretch being localized at 3601 cm Ϫ1 . For each of the larger water clusters (nϭ3,4,5), which have cyclic structures, two absorption bands could be identified, one belonging to the free OH stretch and the other being due to the excitation of the OH ring vibration. The measurements on free water clusters were complemented by studies on small water complexes formed on large argon clusters. The positions of the absorption bands observed in these spectra are close to those found for ͑H 2 O͒ n in argon matrices.

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“…Water trimers are one of the simplest systems where cooperativity is observed, and this property was thoroughly investigated in the literature from a theoretical point of view. 65,66,19 Again, for the case of alcohols this particular problem was much less studied, [53][54][55][56]62,67 mainly because the size of the system increases significantly when hydrogen in water is replaced by alkyl groups. Also of interest are the characteristics of the potential energy surface associated with a given cluster, which are crucial to understand the low-frequency vibrations of the cluster and the mechanisms that connect different enantiomeric forms.…”

Section: Introductionmentioning

confidence: 99%

Study of the methanol trimer potential energy surface

Mó

Yáñez

Elguero

1997

The Journal of Chemical Physics

132

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The potential energy surface of methanol trimer has been studied through the use of high-level ab initio calculations and density functional methods. The geometries have been optimized at the MP2/6-311ϩG(d,p) and B3LYP/6-311ϩG(d,p) levels of theory. The harmonic vibrational frequencies were obtained at the latter level. The final energies for the most stable (CH 3 OH) n (n ϭ1,3) clusters were calculated in the framework of the G2͑MP2,SVP͒ theory. For these and all the other structures the final energies were also obtained using the B3LYP/6-311ϩϩG(3d f ,2p) approach. Three local minima have been located. The global minimum corresponds to a cyclic structure with two methyl groups on one side of the O-O-O plane and the third one on the other side. The bowl conformer, where the three methyl groups are on the same side of the O-O-O plane, is predicted to be only 0.8 kcal/mol less stable than the global minimum. The third local minimum, where one of the monomers behaves as a biacceptor is predicted to lie much higher in energy. Other stationary points associated with a systematic flipping of the methyl groups have been also located. These stationary points, which are transition states or saddle points of higher order, are very close in energy to the global minimum, indicating that the potential energy surface of the methanol trimer is very flat and very similar to that reported before for the water trimer. The calculated enthalpies of association for the dimer and the trimer of methanol are in very good agreement with the experimental values when estimated at the G2͑MP2,SVP͒ level, while they are slightly underestimated when the B3LYP approach is used. The most stable trimer has three different O-H stretching frequencies, in agreement with the experimental evidence. The calculated frequency shifts are only in rough agreement with the experimental values. Cooperative effects are significant in the methanol trimer. They are reflected in larger frequency shifts, greater lengthening of the O-H bonds, shorter O•••O distances than in the dimer. The G2͑MP2,SVP͒ calculated additive interaction energy is also significantly large.

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Molecular orbital study of some protonated bases

Cited by 119 publications

References 11 publications

Proton transfer in ammonia cluster cations: molecular dynamics in a self consistent field

Proton transfer in ammonia cluster cations: molecular dynamics in a self consistent field

Infrared spectroscopy of small size-selected water clusters

Study of the methanol trimer potential energy surface

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