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1.
CNDO/Force calculations have been done for formaldehyde, acetaldehyde and acetone, and the theoretical force fields evaluated. Experimental force fields are obtained from vibrational frequencies using the least-squares refinement method. The initial force fields considered are based on the bending and interaction force constants obtained from the CNDO/Force calculations and the stretching force constants transferred from chemically related molecules. Vibrational frequencies of H2CO, D2CO, HDCO, H213CO and D213CO for formaldehyde, CH3CHO, CH3CDO, CD3CHO, CD3CDO and CH2DCHO for acetaldehyde, and CH3COCH3 CD3COCH3 and CD3COCD3 for acetone are employed in the force field refinements. The final force fields obtained are found to be reasonable with respect to the diagonal and interaction force constants. 相似文献
2.
A new method based on scaled ab initio force fields is introduced for calculating excited-state vibrational frequencies. Application to formaldehyde confirms the need to revise the value of v3 (Ã, H2 CO), but not the value of v3 (ã, D2CO). 相似文献
3.
Aminoborane, H2NBH2 and its isotopologues, H2N10BH2, D2NBD2, and D2N10BD2, have been studied by high-level ab initio methods. All calculations rely on multidimensional potential energy surfaces and dipole moment surfaces including high-order mode coupling terms, which have been obtained from electronic structure calculations at the level of explicitly correlated coupled-cluster theory, CCSD(T)-F12, or the distinguishable cluster approximation, DCSD. Subsequent vibrational structure calculations based on second-order vibrational perturbation theory, VPT2, and vibrational configuration interaction theory, VCI, were used to determine rotational constants, centrifugal distortion constants, vibrationally averaged geometrical parameters and (an)harmonic vibrational frequencies. The impact of core-correlation effects is discussed in detail. Rovibrational VCI calculations were used to simulate the gas phase spectra of these species and an in-depth analysis of the ν7 band of aminoborane is provided. Color-coding is used to reveal the identity of the individual progressions of the rovibrational transitions for this particular mode. 相似文献
4.
Antonio Hidalgo Jos Zúiga Jos M. Francs Adolfo Bastida Alberto Requena 《International journal of quantum chemistry》1991,40(5):685-694
A self-consistent field optimization of the vibrational coordinates for nonlinear triatomic molecules is presented. The optimal coordinates are obtained by making a three-dimensional rotational transformation of the normal modes and determining the rotation angles as those for which the SCF energy is stationary. The utility of the optimized coordinates in full variational calculations of vibrational energies is studied for the molecules of H2O, O3, H2D+, H2T+, and D2T+. For H2O and O3, the optimization procedure leads to the local mode representation. It is shown that the use of the optimal coordinates in variational calculations allows a large reduction of the dimension of the Hamiltonian matrix to be diagonalized in order to reach convergence. 相似文献
5.
《Chemical physics》1987,117(2):295-304
Vibrational excitation by e− impact via low-energy resonances has been investigated in acetaldehyde and acetone and compared with similar results in formaldehyde. Despite the large number of vibrational modes involved, the three systems exhibit a selective excitation of only several modes. Besides an important excitation of the CO stretch modes (dominant in H2CO), excitation of CH stretch, CH3 stretch and CH3 deformation are also observed in CH3CHO and (CH3)2CO. Interpretation of the energy loss spectra is given in terms of recently developed symmetry considerations together with the character of the LUMO occupied by the extra electron to form the transitory negative ion (resonance). Differential cross sections versus electron energy are presented for elastic and several inelastic processes. Weak oscillations (of the “boomerang” type) are observed on the inelastic cross sections for acetaldehyde, whereas no structure appears for acetone. This is in contrast with the pronounced oscillations observed for H2CO, and reveals a shorter lifetime for the CH3CHO− and (CH3)2CO− resonant states, compared to H2CO−. 相似文献
6.
Daniel Strobusch Mathias Nest Christoph Scheurer 《Journal of computational chemistry》2013,34(14):1210-1217
The hierarchical expansion of the kinetic energy (HEKE) operator in curvilinear coordinates presented recently (Strobusch and Scheurer, J. Chem. Phys. 2011a, 135, 124102; Strobusch and Scheurer, J. Chem. Phys. 2011b, 135, 144101) relies on a many‐body expansion of the metric tensor. It is shown how this expansion can be adapted to a specific system. An analytic formula is derived, which yields an estimate of the impact of a certain expansion term on the spectrum. In combination with the hierarchical structure of the many‐body expansion and interpolation techniques, the memory consumption and evaluation time of the HEKE operator as well as the computational costs for subsequent vibrational self‐consistent field and vibrational configuration interaction calculations are reduced significantly, which is demonstrated by studies on two small test systems H2O2 and formaldehyde (H2CO). © 2013 Wiley Periodicals, Inc. 相似文献
7.
John B. Marling 《Chemical physics letters》1975,34(1):84-89
Highly selective isotope separation of deuterium has been demonstrated in laser-irradiated formaldehyde mixtures of H2CO and HDCO. Single step deuterium enrichment factors of 14 were achieved by photodissociation into HD and CO, using HeCd laser light at 325.03 nm. Initial deuterium concentration ranged from 0.015 mole percent (natural abundance) to 5 mole percent. 相似文献
8.
A computer program SURVIB is described for calculating vibrational anharmonicity constants for polyatomic molecules. The program requires as input a grid of calculated energies in the vicinity of a stationary point. This grid is fit, in a least squares sense, to a polynomial function of the internal coordinates. This analytic representation of the energy surface is employed in a normal mode analysis, and the energy is reexpanded as a polynominal function of the normal mode coordinates (expressed as vectors in the mass-weighted atomic Cartesian coordinate space). The resulting coefficients are used in a second-order perturbation theory analysis to obtain the vibrational anharmonicity constants. Also reported is an application of this program to formaldehyde employing ab initio, RHF , MP 2, MP 3, and RHF -CI calculations. The spectroscopic constants obtained for H2CO are in good agreement with experimentally derived values recently reported by Reisner. 相似文献
9.
《Chemical physics》1987,111(1):87-95
The structures and energies of various LiC2H2 complexes have been investigated by means of ab initio molecular orbital calculations. Analytic SCF gradients were employed with a double-ζ basis set to locate and characterize stationary points on the energy surface. Single-point CI calculations using a double-ζ + diffuse and polarization basis set have been carried out at the DZ + P SCF stationary points. With the highest-level theory, the Li—vinylidene complex and the cis bridged adduct are found to be the most favorable arrangements, the former complex being slightly more stable by about 2 kcal mol−1. These molecules are bound respectively by about 5 and 3 kcal mole−1 relative to infinitely separated lithium plus acetylene. Harmonic vibrational frequencies are also reported and confirm the existence of the cis LiC2H2 species recently observed in a solid argon matrix. 相似文献
10.
V. Adamantides 《Chemical physics》1980,48(2):221-225
SCF closed shell calculations were performed to determine the equilibrium structure and vibrational frequencies of the O4 molecule by means of Payne's method and with the help of the molecule's symmetry coordinates. The equilibrium geometry corresponds to symmetry group D2d with R = 1.505 Å and h = 0.094 Å. The vibrational frequencies are: ν5(E) = 885.5 cm?1, ν3(B1) = 1051.9 cm?1, ν1(A1) = 1018.3 cm?1, ν4(B2) = 880.3 cm?1. The second vibrational coordinate (A1) corresponds to a double-well potential. The first vibrational levels were calculated by a variational method. 相似文献
11.
A potential energy surface for the ground X? 1A1 state of H2CO has been derived, which reproduces the position of a recently calculated H2 + CO transition state. The variational method for the determination of frequencies of potential energy surfaces has been extended to tetra-atomics, thus enabling the surface to be refined. 相似文献
12.
Ab initio quantum chemical calculations (MP2/4–31G**) were performed for the dihydrogen elimination reaction from protonated formaldehyde. The energy difference between reactants and products and the activation energies were found to be in good agreement with the corresponding experimental quantities. Theoretical rate vs. energy curves were computed for a series of isotopic variants of the reaction using the Rice–Ramsperger–Kassel–Marcus (RRKM) method. The vibrational frequencies used in these calculations were taken from the 4–31G** geometry-optimized transition state and reactant structures. Quantum mechanical tunnelling was introduced to explain the existence of metastable CH2OH ions, and a negative kinetic shift of about 0.1 eV was found. The intramolecular kinetic isotope effect for loss of HH/HD and DH/DD was calculated and compared with the experimental data. The result is consistent with the assumption that the average internal energy of metastable [CH2OH]+ ions is very close to the critical energy for H2 loss. 相似文献
13.
The study of D2O isolated in amorphous H2O (ice Iv) has been extended to the determination of the bending mode frequency (1230 cm?1) and to the measurement of the vibrational spectrum of the cubic ice phase (ice Ic). The vibrationally decoupled stretching frequencies (ν1 = 2367 cm?1 and ν3 = 2444 cm?1) for D2O in the H2O (Ic) have been obtained and an estimate of the exchange activation energy is given. 相似文献
14.
M. Gerhards K. Beckmann K. Kleinermanns 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1994,29(3):223-229
Ab initio calculations at the Hartree-Fock 4-31G* level were performed in order to calculate binding energies and vibrational frequencies of the phenol/CH3OH-cluster and two deuterated isotopomers (d-phenol/CH3OD,d-phenol-CD3OD). The minimum energy structure is trans-linear, as for the phenol/H2O-cluster. The calculated frequencies of phenol and methanol as well as the intramolecular frequencies of the phenol/CH3OH-cluster are assigned to experimental values. The calculated intermolecular frequencies of the phenol/CH3OH-cluster are compared with the available experimental frequencies of theS 0 (andS 1)-state of the phenol/methanol-cluster and the similarp-cresol/methanol-cluster. Assignments are suggested for the σ andp 1-mode. In order to clarify the assignment of the low frequency vibration at 22 cm?1 anharmonic corrections for the β2-mode of the phenol/CH3OH-cluster are calculated. These calculations show only slight anharmonicity compared with the β2-mode calculations carried out for the phenol/H2O-cluster. 相似文献
15.
Model calculations have been made of the vibrational frequencies and normal modes of a water molecule vibrating in a combined internal and external field. A constant internal force field has been used together with an external central force field from four or three nearest-neighbour atoms to the water molecule. These neighbour atoms have been arranged either tetrahedrally or trigonally around the water molecule. The external force field has been further restricted by the use of five possible site symmetries for the water molecule, C2v, C2, Cs(σxz, Cs(σyz) and C1. A series of calculations have been made where the external force constants have been varied within the range 1—80 Nm?1.The nine calculated normal modes can be divided into three groups: intra-molecular, rotational and translational vibrations. Among the rotational vibrations it is found that, in the tetrahedral environment, the rocking mode occurs at lower frequencies than the twisting and wagging modes, whereas the opposite occurs for the trigonal environment. Frequency ratios have been calculated using the isotopic species H2O, D2O, HDO and H,18O. The twisting and wagging modes have the vH2O/vD2O ratio in the range 1.35-3-1.41 and the rocking mode in the range 1.26—1.41. 相似文献
16.
Using laser-induced fluorescence in a low-pressure flow system, the lifetimes of the 0010 and 1010 vibrational levels of the B2Πi state of NCO have been measured. The results, 63 and ≤10 ns respectively, indicate that the dissociation limit to N(2D) + CO lies between these levels. This corresponds to a dissociation energy D00 ≤ 1.68 eV and an enthalpy of formation ΔHf,2980 ? 48 kcal/mole for NCO, and ΔHf,2980 (HNCO) ? ?14 kcal/mole. 相似文献
17.
B.J. Van Der Veken 《Journal of Molecular Structure》1975,25(1):75-99
The vibrational spectra (IR and Raman) of CH2ClPO3H2 and of its anions in solutions of H2O and D2O are reported. The IR spectra of the solid dibasic sodium and potassium salts, the solid normal and O-deuterated monobasic sodium and potassium salts and of the solid normal and O-deuterated acid are discussed. Symmetry and internal stretching force constants, stretch-stretch interactions and potential energy distributions are obtained from normal coordinate analysis of CH2C1PO3H2, CH2ClPO3H? and CH2C1PO32?, and the calculated and observed frequencies for O-deuterated acid and monobasic anion are compared. 相似文献
18.
Time-dependent close coupling for vibrational excitation in three dimensions: Application to H+ - H2
Reinhard Schinke 《Chemical physics》1977,24(3):379-389
Impact parameter calculations for the non-reactive H+ + H2 (ni = 0) → H+ + H2 (nf) collision are reported for energies 10 eV ? Ecm ? 200 eV describing the rotational motion of the molecule in the sudden limit. The time-dependent Schrödinger equation for the vibrational motion has been solved by close coupling techniques expanding the vibrational wavefunction into both harmonic and numerically exact H2 bound states. The convergence in vibrational basis sets, where up to six vibrational levels are considered, becomes worse with decreasing energy and increasing inelasticity. Furthermore, the harmonic wavefunctions are not suitable over a large range of energies to calculate proper cross sections. The various integral and differential cross sections have been compared with the classical results of Giese and Gentry. 相似文献
19.
Reactions of Group V Metal Atoms with Hydrogen Sulfide:Argon Matrix Infrared Spectra and Theoretical Calculations
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The reaction of laser-ablated vanadium, niobium and tantalum atoms with hydrogen sulfide has been investigated using matrix isolation FTIR and theoretical calculations. The metal atoms inserted into the H-S bond of H2S to form the HMSH molecules (M=V, Nb, Ta), which rearranged to H2MS molecules on annealing for Nb and Ta. The HMSH molecule can also further react with another H2S to form the H2M(SH)2 molecules. These new molecules were identified on the basis of the D2S and H234S isotopic substitutions. DFT (B3LYP and BPW91) theoretical calculations are used to predict energies, geometries, and vibrational frequencies for these novel metal dihydrido complexes and molecules. Reaction mechanism for formation of group V dihydrido complex was investigated by DFT internal reaction coordinate calculations. The dissociation of HVSH gave VS+H2 on broad band irradiation and reverse reaction happened on annealing. Based on B3LYP calculation releasing hydrogen from HVSH is endothermic only by 13.5 kcal/mol with lower energy barrier of 16.9 kcal/mol. 相似文献
20.
Grady D. Carney 《Chemical physics letters》1981,78(1):200
Ab initio calculated values of fundamental vibrational frequencies and zero-point energies are presented for HTD+, D2T+, T2D+, H2T+, T2H+ and T+3. 相似文献