Theoretical study of the electric dipole moment function of the ClO molecule

The high resolution rovibrational spectrum of H2S has been evaluated from three-dimensional ab initio potential energy and electric dipole moment functions and variational rovibrational eigenfunctions, which took full account of anharmonicity effects and rotation–vibration coupling. The quality of the near equilibrium theoretical potential energy function has been checked by comparisons with experimental equilibrium structure, empirical quartic force fields, vibrational band origins, centrifugal distortion constants, and rotational energy levels. All parameters agree well with the available experimental data. Vibrational band intensities for the ν2, 2ν2, ν1, and ν3 bands have been calculated from empirical and ab initio dipole moment functions and compared with experimental and theoretical integrated band intensities. The difficulties arising by the derivation of such data from the experimental intensities of H2S are discussed. The theoretical results strongly suggest that higher than first derivatives are needed for a proper description of the dipole moment function. The room temperature absorption spectra have been evaluated ab initio for the pure rotational and the ν2, 2ν2, ν1, and ν3 transitions. The unusual intensity pattern of the P, Q, and R branches attributed to the rotational–vibrational coupling has been well reproduced. Absolute line intensities calculated previously by perturbation theory are compared with variational results. The purely theoretical line intensities agree satisfactorily with experiment for the bending transitions, however, the extremely flat regions of the dipole moment functions along the bond stretching displacements make the transition intensities very sensitive to the values of the dipole moment derivatives.

Potential energy, electric dipole, and electronic transition moment functions have been calculated for several bound electronic states of CH− and NH− from accurate electronic wave functions. Spectroscopic constants for the X 2Π state of NH− have been compared with the data recently obtained by laser induced autodetachment spectroscopy. Spectroscopic constants of the A 2Σ+ state of NH− and radiative X 2Π–A 2Σ+ transition probabilities are presented. Spectroscopic constants and infrared transition probabilities for the X 3Σ− and the a 1Δ states of CH− have been calculated. The radiative lifetime of v=1 in CH−(X 3Σ−) is found to be in a very good agreement with a recent experimental value. The transition probabilities are for both ions much larger than those of their neutral counterparts, and increase in the series OH−, NH−, CH−.

Ab initio calculations employing the coupled cluster method CCSD(T), in conjunction with a small-core pseudopotential for the cadmium atom, have been employed to construct a near-equilibrium potential energy function (PEF) and an electric dipole moment function (EDMF) for CdH(2). The significance of the spin-orbit interaction was checked and found to be of minor importance. Making use of two pieces of experimental information for the most abundant isotopomer (114)CdH(2), we obtained a refined PEF, which, within variational calculations of rovibrational states and wave functions, reproduces all available experimental data (S. Yu, A.Shayesteh, and P. F. Bernath, J. Chem. Phys. 2005, 122, 194301) very well. In addition, numerous predictions are made. In particular, the nu(2) band origins for (114)CdH(2) and (114)CdD(2) are predicted at 605.9 and 436.9 cm(-1), respectively, and the state perturbing the e parity levels of the (0,0(0),1) state of (114)CdH(2) at J = 12-17 is identified as the (0,3(3),0) state. Assignments for further perturbations found in the emission spectra are given as well.

We applied cavity-enhanced frequency modulation absorption spectroscopy (also known as noise-immune cavity-enhanced optical heterodyne molecular spectroscopy) to perform high-resolution spectroscopy of the sixth overtone band of nitric oxide near 797 nm. By using novel high-bandwidth balanced detectors, baseline variations caused by residual amplitude modulation were significantly reduced. The ultrahigh sensitivity (2 x 10(-10) cm(-1) minimum detectable absorption at 1 Hz detection bandwidth) of our spectrometer allowed accurate measurements of 15 individual line intensities of P- and R-branch transitions in the 2Pi(1/2)-2Pi(1/2) subband. A vibrational transition moment of 3.09(6) muD+/-13% and Herman-Wallis coefficients of a = -0.0078(26) and b = 0.001 25(45) were found by fitting the line intensities. Based on our measured transition moment, and those of other transitions from the literature, a new parametrization for the electric dipole moment function (EDMF) of nitric oxide, valid for 0.91 < or = r < or = 1.74 A, has been extracted. The residuals of this fit demonstrate that the derived EDMF is the most accurate representation to date of the dipole moment function. The new EDMF will be valuable for accurate intensity prediction of transitions that cannot be easily measured experimentally.

Electric field gradients (efg’s) at the nitrogen nuclei in N2, NO+, NO, CN, and CN− and at the nitrogen and hydrogen nuclei in HCN, HNC, and NH3, calculated using ab initio quantum chemical methods, are reported. Employing extensive Gaussian basis sets, the efg’s were computed at the self-consistent field (SCF), singles and doubles configuration interaction [CI(SD)], and coupled pair functional (CPF) levels of theory as the expectation values of the efg operator and also as the energy derivatives of the appropriate perturbed Hamiltonian using the finite field method. Corrections due to zero point vibrational motions were also calculated. The effect of basis set incompleteness on the calculated efg’s, together with the experimental nuclear quadrupole coupling constants, are used to estimate the 14N and 2H nuclear quadrupole moments, and to test the quality of the correlated wave functions generated by the CI(SD) and CPF methods. The recommended values, on the basis of the present calculations, are 2.05±0.02 and 0.29±0.01 fm2, respectively, for the 14N and 2H quadrupole moments.

A b initio calculations have been carried out on the stretching potential energy surfaces of OCS and the isoelectronic positive ion OCCl+. The methods used included fourth order Mo/ller–Plesset perturbation theory with single, double, and quadruple substitutions (MP4SDQ), singles and doubles configuration interaction (CI-SD), and the latter with the addition of a size-consistency correction [designated CI-SD(s)]. Identical calculations were also carried out on the diatomics CO, CS, and CCl+, and these results were used to correct the CI-SD(s) potential energy functions of OCS and OCCl+. Stretching vibrational band origins have been calculated variationally for both OCS and OCCl+, and those for OCS obtained from the corrected CI-SD(s) potential function are within 0.4% of experiment for transitions up to 5000 cm−1. The ground state rotational constant of OCCl+ is predicted to be 5955±15 MHz, while the band origins of the ν1 and ν3 stretching fundamentals are predicted to lie at 793(10) and 2282(20) cm−1, respectively. Electric dipole moments have been calculated from the CI-SD wave functions, and rotationless dipole moment matrix elements have been derived from the analytical dipole moment functions and the vibrational wave functions obtained from the variational calculations. The ν3 band of OCCl+ is predicted by CI-SD to be fairly strong with a band strength of 1490 cm−2 atm−1, while the ν1 band is weaker by more than 1 order of magnitude.

Momentum profiles for open shell molecules: studies of the HOMOs of NO, O2 and NO2 by electron momentum spectroscopy and SCF, post-Hartree-Fock and DFT calculations

Using the density functional B3P86/cc-PV5Z method, the geometric structure of BH molecule under different external electric fields is optimized, and the bond lengths, dipole moments, vibration frequencies, and other physical properties parameters are obtained. On the basis of setting appropriate parameters, scanning single point energies are obtained by the same method and the potential energy curves under different external fields are also obtained. These results show that the physical property parameters and potential energy curves may change with external electric field, especially in the case of reverse direction electric field. The potential energy function without external electric field is fitted by Morse potential, and the fitting parameters are obtained which are in good agreement with experimental values. In order to obtain the critical dissociation electric parameter, the dipole approximation is adopted to construct a potential model fitting the corresponding potential energy curve of the external electric field. It is found that the fitted critical dissociation electric parameter is consistent with numerical calculation, so that the constructed model is reliable and accurate. These results will provide important theoretical and experimental reference for further studying the molecular spectrum, dynamics, and molecular cooling with Stark effect.

It was proposed that iron hydride, FeH, would be formed only on grains at the clouds through the reaction of the adsorbed H atoms or H2 molecules with the adsorbed Fe atoms on the grains. The importance of FeH in Astrophysics presents an additional motivation to study its energetic, spectroscopic constants and Potential Energy Curves. The structural optimization for ground state of FeH was calculated by different theoretical methods, namely, Hartree-Fock (HF), the density functional theory (DFT), B3LYP, MP2 method and QCISD(T) methods and compared with available data from the literature. The single ionized forms, cation and anion, were also obtained at the same level of calculations. Charges, dipole moment, geometrical parameters, molecular orbital energies and spectroscopic parameters were calculated and reported. In addition, the molecular ionization potential, electron affinity and dissociation energy were investigated.

Quantum chemistry has become one of the most reliable tools for characterizing the thermochemical underpinnings of reactions, such as bond dissociation energies (BDEs). The accurate prediction of these particular properties (BDEs) are challenging for ab initio methods based on perturbative corrections or coupled cluster expansions of the single-determinant Hartree-Fock wave function: the processes of bond breaking and forming are inherently multi-configurational and require an accurate description of non-dynamical electron correlation. To this end, we present a systematic ab initio approach for computing BDEs that is based on three components: 1) multi-reference single and double excitation configuration interaction (MRSDCI) for the electronic energies; 2) a two-parameter scheme for extrapolating MRSDCI energies to the complete basis set limit; and 3) DFT-B3LYP calculations of minimum-energy structures and vibrational frequencies to account for zero point energy and thermal corrections. We validated our methodology against a set of reliable experimental BDE values of CC and CH bonds of hydrocarbons. The goal of chemical accuracy is achieved, on average, without applying any empirical corrections to the MRSDCI electronic energies. We then use this composite scheme to make predictions of BDEs in a large number of hydrocarbon molecules for which there are no experimental data, so as to provide needed thermochemical estimates for fuel molecules.

Potential energy and dipole moment functions have been calculated for the first two excited electronic states of CO by several ab initio methods using large Gaussian basis sets. Similar calculations on the ground state have also been performed to provide a basis for comparison. The types of calculations on the a 3Π state included complete active space self-consistent field (CASSCF), single reference single and doubles configuration interaction (CI-SD) including a size consistency correction [CI-SD(s)], quadratic CI-SD (QCI-SD), and quadratic CI-SD including the effects of triple excitations [QCI-SD(T)], and version 1 of the coupled electron pair approximation (CEPA-1).The best calculated dipole moment functions for the a 3Π state have been found to be consistent with earlier theoretical results with respect to shape (slope, μ′e), and also more accurate in predicting the equilibrium value μe. Theoretical dipole moment functions for the a′ 3Σ+state are presented for the first time, at the CI-SD, CI-SD(s), and CASSCF levels of approximation. The first two of these yield estimates of μe that are in very good agreement with that derived from the analysis of perturbations in the molecular beam electric resonance (MBER) Stark effect of the a 3Π state. The (a–a′) electronic transition moment has also been calculated at the CASSCF and CI-SD levels. Our CASSCF value of 0.23 D (v″=4, v′=0) compares well with values derived from the MBER Stark effect.

Line lists for the b1Σ+-X3Σ− and a1Δ-X3Σ− transitions of SO

Using pulsed laser photolysis (PLP) and laser-induced fluorescence (LIF) we have studied the formation of O2(X3Σg-) in high vibrational levels when O3 is photolysed at 266 nm. Experiments have been performed in both Ar and N2 diluents. In the former, O2(X3Σg-) in high vibrational levels is formed primarily as a product of the reaction between O(1D) atoms and O3: O(1D)+O3→2 O2(X3Σg-, v). In a large excess of N2, the O(1D) atoms are quenched and one only observes the O2(X3Σg-) molecules created by direct photolysis in the ‘triplet channel’: O3+hν (λ=266 nm)→O2(X3Σg-, v)+O(3P). Employing LIF in the (0, v) and (2, v) bands of the O2 (B 3Σu-–X3Σg-) system, we have characterised the nascent vibrational distributions from both these processes for 18⩽v⩽23. In addition, by observing how the population in specific vibrational levels changes with time, we have determined rate constants for vibrational relaxation of O2(X3Σg-, v=21 and 22) with He, O2, N2, CO2, N2O and CH4. The results are compared with those obtained in other studies for relaxation from the same and other levels of O2(X3Σg-) and the implications of the results for atmospheric chemistry are discussed.

Molecular structures and energies have been computed at the double zeta SCF level for several linear triple bonded molecules that are either isomers or protonated forms of the familiar molecules cyanoacetylene and cyanogen. These structures have been used to predict rotational constants that can be used as a guide for locating or assigning laboratory or astrophysical microwave spectra. For the same molecules the dipole moments have been computed at the double zeta plus polarization configuration interaction level. Similar structure and dipole moment calculations have also been done on several related known molecules to assess the accuracy of the numerical results. All of the computed dipole moments fit into a pattern that can be roughly explained by simple polarization arguments.

Using the density functional B3P86/cc-PV5Z method, the geometric struc- ture of AlH molecule under different external electric fields are optimized, and the bond lengths, dipole moments, vibration frequencies and other physical properties parameters are obtained. The potential energy curves under different external fields are also obtained by CCSD(T) method with the same basis set. These results show that the properties parameters and potential energy curves may change with different external electric field, especially in the reverse electric fields. The potential energy function without external electric field is fitted by Morse potential, and the poten- tial energy curves under different external fields are fitted using constructed potential model, which adopted the dipole approximation theory. It is found that the fitting parameters are good agreement with experimental values and the critical dissociation electric parameter is consistent with numerical calculation. These results will provide important theoretical and experimental reference for further studying the molecular spectrum, dynamics and molecular cooling with Stark effect.