Ground State Dissociation Energy Research Articles

Excitation spectra of CdRg (Rg = He, Ne, Xe) complexes recorded at the [formula omitted] transition: From the heaviest CdXe to the lightest CdHe

Laser-induced fluorescence excitation spectra of CdRg (Rg = He, Ne, Xe) complexes were recorded at the D 1 Σ 0 + ← X 1 Σ 0 + bound ← bound and free ← bound transitions. In case of CdXe, analysis of the recorded profiles resulted in determination of the D 1 Σ 0 + -state potential energy curve and ground-state dissociation energy. In case of CdHe and CdNe, analysis of the free ← bound profiles provided a repulsive part of the D 1 Σ 0 + -state potential. Valence ab initio calculations of the ground- and excited-state potentials and electronic transition dipole moments of the studied transition were performed taking scalar-relativistic and spin-orbit effects into account. The results were supplemented with those for CdAr and CdKr of our earlier study.

Nonadiabatic corrections to the wave function and energy

Nonadiabatic corrections in molecules composed of a few atoms are considered. It is demonstrated that a systematic perturbative expansion around the adiabatic solution is possible, with the expansion parameter being the electron-nucleus mass ratio to the 3/4 power. Closed form formulas for the leading corrections to the wave function and to the energy are derived. Their applicability is demonstrated by a comparison of numerical results for the hydrogen molecule with the former nonadiabatic calculations and the experimental values. Good agreement with the recent experiment is achieved for the ground state dissociation energy of both H(2) and D(2).

Ground State Potential Energy Curve and Dissociation Energy of MgH

New high-resolution visible emission spectra of the MgH molecule have been recorded with high signal-to-noise ratios using a Fourier transform spectrometer. Many bands of the A 2Pi-->X 2Sigma+ and B' 2Sigma+-->X 2Sigma+ electronic transitions of 24MgH were analyzed; the new data span the v' = 0-3 levels of the A 2Pi and B'2Sigma+ excited states and the v''=0-11 levels of the X 2Sigma+ ground electronic state. The vibration-rotation energy levels of the perturbed A 2Pi and B' 2Sigma+ states were fitted as individual term values, while those of the X 2Sigma+ ground state were fitted using the direct-potential-fit approach. A new analytic potential energy function that imposes the theoretically correct attractive potential at long-range, and a radial Hamiltonian that includes the spin-rotation interaction were employed, and a significantly improved value for the ground state dissociation energy of MgH was obtained. The v''=11 level of the X 2Sigma+ ground electronic state was found to be the highest bound vibrational level of 24MgH, lying only about 13 cm(-1) below the dissociation asymptote. The equilibrium dissociation energy for the X 2Sigma+ ground state of 24MgH has been determined to be De=11104.7+/-0.5 cm(-1) (1.37681+/-0.00006 eV), whereas the zero-point energy (v''=0) is 739.11+/-0.01 cm(-1). The zero-point dissociation energy is therefore D0=10365.6+/-0.5 cm(-1) (1.28517+/-0.00006 eV). The uncertainty in the new experimental dissociation energy of MgH is more than 2 orders of magnitude smaller than that for the best value available in the literature. MgH is now the only hydride molecule other than H2 itself for which all bound vibrational levels of the ground electronic state are observed experimentally and for which the dissociation energy is determined with subwavenumber accuracy.

XΣ+1andaΣ+3states of LiCs studied by Fourier-transform spectroscopy

We present the first high-resolution spectroscopic study of LiCs. LiCs is formed in a heat-pipe oven and studied via laser-induced fluorescence Fourier-transform spectroscopy. By exciting molecules through the $X\phantom{\rule{0.2em}{0ex}}^{1}\ensuremath{\Sigma}^{+}\text{\ensuremath{-}}B\phantom{\rule{0.2em}{0ex}}^{1}\ensuremath{\Pi}$ and $X\phantom{\rule{0.2em}{0ex}}^{1}\ensuremath{\Sigma}^{+}\text{\ensuremath{-}}D\phantom{\rule{0.2em}{0ex}}^{1}\ensuremath{\Pi}$ transitions vibrational levels of the $X\phantom{\rule{0.2em}{0ex}}^{1}\ensuremath{\Sigma}^{+}$ ground state have been observed up to $3\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ below the dissociation limit enabling an accurate construction of the potential. Furthermore, rovibrational levels in the $a\phantom{\rule{0.2em}{0ex}}^{3}\ensuremath{\Sigma}^{+}$ triplet ground state have been observed via singlet-triplet mixing in the higher excited states. With the help of coupled channels calculations, accurate singlet and triplet ground-state potentials were derived reaching the atomic ground-state asymptote. These potentials yield an accurate determination of the singlet and triplet ground-state dissociation energies and allow first predictions of cold collision properties of $\mathrm{Li}+\mathrm{Cs}$ pairs.

Quantum Monte Carlo studies on small molecules

The Variational Monte Carlo (VMC) and Fixed-Node Diffusion Monte Carlo (FNDMC) methods have been examined, through studies on small molecules. New programs have been written which implement the (by now) standard algorithms for VMC and FNDMC. We have employed and investigated throughout our studies the accuracy of the common Slater–Jastrow trial wave function. Firstly, we have studied a range of sizes of the Jastrow correlation function of the Boys–Handy form, obtained using our optimization program with analytical derivatives of the central moments in the local energy. Secondly, we have studied the effects of Slater-type orbitals (STOs) that display the exact cusp behaviour at nuclei. The orbitals make up the all important trial determinant, which determines the fixed nodal surface. We report all-electron calculations for the ground state energies of Li2, Be2, H2O, NH3, CH4 and H2CO, in all cases but one with accuracy in excess of 95%. Finally, we report an investigation of the ground state energies, dissociation energies and ionization potentials of NH and NH+. Recent focus paid in the literature to these species allow for an extensive comparison with other ab initio methods. We obtain accurate properties for the species and reveal a favourable tendency for fixed-node and other systematic errors to cancel. As a result of our accurate predictions, we are able to obtain a value for the heat of formation of NH, which agrees to within less than 1 kcal mol−1 to other ab initio techniques and 0.2 kcal mol−1 of the experimental value.

Relativistic configuration interaction study of the electronic spectrum of SnTe and SnTe+

Ab initio based relativistic configuration interaction calculations have been performed to study the electronic spectrum of the heaviest tin chalcogenide and its monopositive ion. Potential energy curves and spectroscopic constants of low-lying states of both species within 7 eV are reported. The ground-state dissociation energies of SnTe and SnTe+ are computed to be 3.48 and 2.50 eV, respectively. The spin-orbit splitting between the two components of the X 2Pi state of SnTe+ is about 3030 cm(-1). Effects of the strong spin-orbit coupling on the potential curves and spectroscopic properties of both the species are investigated in detail. The electric dipole moments of some of the low-lying states of SnTe and SnTe+ are reported. Transition moments of some important spin-allowed and spin-forbidden transitions are calculated from the configuration interaction wave functions. The radiative lifetime of the excited E 1sigma0+(+) state of SnTe is about 39 ns. The X2-X1 transition in SnTe+ is found to be more probable than the similar transition in the lighter ions. The vertical ionization energy of SnTe in the ground state is estimated to be 8.22 eV.

Configuration interaction study of the electronic spectrum of SnSe +

The electronic spectrum of SnSe + has been studied from the ab initio based multireference configuration interaction calculations which include relativistic effective core potentials of both the atoms. Potential energy curves of all 12 low-lying states, which dissociate into the lowest asymptote Sn +( 2P u) + Se( 3P g), have been constructed. The ground-state dissociation energy is estimated to be 2.74 eV. Spectroscopic constants of eight low-lying states of SnSe + within 25 000 cm −1 of energy are computed. The electronic states, which include the spin–orbit coupling, have also been investigated. The ground-state spin–orbit splitting is about 1840 cm −1. The radiative lifetimes of B 2Σ +, A 2Σ +, and 2 2Π states of SnSe + are calculated. The effect of the spin–orbit coupling on the A 2Σ +–X 2Π transition has been studied in details. The electric dipole moments of the ion in the low-lying states are reported. The vertical ionization energy of the ground-state SnSe is about 8.93 eV.

Multireference calculations of the electronic structure of VF2 and VCl2

We investigated the electronic structure of two members of the transition-metal dihalide family, VF(2) and VCl(2). Using the configuration-interaction method in large basis sets we calculated the lowest 17 states of these molecules in the vicinity of their ground-state geometry. We compute the ground-state bond lengths, vibrational frequencies, and dissociation energies. In contrast to predictions of ligand-field theory, we find (4)Sigma(g) (-) ground states for both molecules.

Improved Morphed Potentials for Ar−HBr Including Scaling to the Experimentally Determined Dissociation Energy

A lead salt diode infrared laser spectrometer has been employed to investigate the rotational predissociation in Ar-HBr for transitions up to J' = 79 in the v(1) HBr stretching vibration of the complex using a slit jet and static gas phase. Line-shape analysis and modeling of the predissociation lifetimes have been used to determine a ground-state dissociation energy D(0) of 130(1) cm(-1). In addition, potential energy surfaces based on ab initio calculations are scaled, shifted, and dilated to generate three-dimensional morphed potentials for Ar-HBr that reproduce the measured value of D(0) and that have predictive capabilities for spectroscopic data with nearly experimental uncertainty. Such calculations also provide a basis for making a comprehensive comparison of the different morphed potentials generated using the methodologies applied.

Electronic States of SnS and SnS+: A Configuration Interaction Study

Ab initio based multireference configuration interaction calculations are carried out for SnS and its monopositive ion using effective core potentials. Potential energy curves and spectroscopic constants of the low-lying states of SnS and SnS+ are computed. The ground-state dissociation energies of the neutral and ionic species are about 4.71 and 2.86 eV, respectively which compare well with the available thermochemical data. The effect of d-electron correlation on the spectroscopic constants of a few low-lying states has been studied. The spin-orbit interaction has also been included to investigate its effect on the spectroscopic properties of both SnS and SnS+. Dipole moment and transition moment curves are also constructed as a function of the bond length. Transition probabilities of some dipole-allowed and spin-forbidden transitions are studied. Radiative lifetimes of a few low-lying states are estimated. The E1sigma+-X1sigma+ transition of SnS is predicted to be the strongest one. The components of the A2sigma(+)(1/2)-X2(2)pi(1/2) transition with parallel and perpendicular polarization are separately analyzed. The vertical ionization energies of the ground-state SnS to the ground and low-lying excited states of the monopositive ion are calculated.

Theoretical studies of the electronic spectrum of SnSe

Multireference configuration interaction calculations are performed on the SnSe molecule to study its electronic spectrum within 5 eV of energy. Potential energy curves of the ground and low-lying electronic states, which correlate with the lowest dissociation limit, are constructed. Spectroscopic constants ( T e, r e, ω e) of nine bound states of SnSe are reported. The ground-state dissociation energy is estimated to be 4.38 eV. The spin–orbit interaction has also been included in the calculation. Transition dipole moments of several dipole-allowed and spin-forbidden transitions are computed. Transitions such as E 1 Σ 0 + + – X 1 Σ 0 + + and D 1 Π 1 – X 1 Σ 0 + + are found to be more probable. The radiative lifetimes of A 0 + – X 1 Σ 0 + + and B 1 – X 1 Σ 0 + + are predicted to be about 11 and 130 μs, respectively. Dipole moments of the ground and low-lying states are estimated and compared with observed data.

Estimation of dissociation energy of NiC molecule

The experimental potential-energy curve for the electronic ground state of an astrophysically important NiC molecule is constructed by applying the Rydberg–Klein–Rees method as modified by Vanderslice et al. The ground state dissociation energy is estimated by a curve-fitting technique using the modified Lippincott potential function, and this estimated value of D 0 = 3.454 eV is in good agreement with the value of D 0 ⩾ 3.34 eV reported by Brugh and Morse.

Spectroscopic studies of atmospheric interest on NO and NO +

In recent years, high-resolution photoelectron spectroscopy and ab initio calculations have considerably revised and enlarged the understanding of the electronic structure of the NO and NO + molecules. The experimental potential energy curves for the different electronic states of atmospheric interest molecules like NO and NO + are constructed by using the Rydberg–Klein–Rees method as modified by Vanderslice et al. The ground state dissociation energies are determined by curve fitting technique using the five parameter Hulburt–Hirschfelder (H–H) function. The estimated dissociation energies are 6.381 and 10.693 eV for NO and NO +, respectively. These values are in good agreement with the literature values. The r-centroids and Franck–Condon factors (FC Factors) for the band system of B 2Π r –X 2Π of NO and a 3Σ +–X 1Σ +, A 1Π–X 1Σ + of NO + molecules have been calculated employing an approximate analytical methods of Jarmain and Fraser, and Nicholls and Jarmain. The absence of the bands in these systems is explained.

Probing the Watson−Crick, Wobble, and Sugar-Edge Hydrogen Bond Sites of Uracil and Thymine

The nucleobases uracil (U) and thymine (T) offer three hydrogen-bonding sites for double H-bond formation via neighboring N-H and C=O groups, giving rise to the Watson-Crick, wobble and sugar-edge hydrogen bond isomers. We probe the hydrogen bond properties of all three sites by forming hydrogen bonded dimers of U, 1-methyluracil (1MU), 3-methyluracil (3MU), and T with 2-pyridone (2PY). The mass- and isomer-specific S1 <-- S0 vibronic spectra of 2PY.U, 2PY.3MU, 2PY.1MU, and 2PY.T were measured using UV laser resonant two-photon ionization (R2PI). The spectra of the Watson-Crick and wobble isomers of 2PY.1MU were separated using UV-UV spectral hole-burning. We identify the different isomers by combining three different diagnostic tools: (1) Selective methylation of the uracil N3-H group, which allows formation of the sugar-edge isomer only, and methylation of the N1-H group, which leads to formation of the Watson-Crick and wobble isomers. (2) The experimental S1 <-- S0 origins exhibit large spectral blue shifts relative to the 2PY monomer. Ab initio CIS calculations of the spectral shifts of the different hydrogen-bonded dimers show a linear correlation with experiment. This correlation allows us to identify the R2PI spectra of the weakly populated Watson-Crick and wobble isomers of both 2PY.U and 2PY.T. (3) PW91 density functional calculation of the ground-state binding and dissociation energies De and D0 are in agreement with the assignment of the dominant hydrogen bond isomers of 2PY.U, 2PY.3MU and 2PY.T as the sugar-edge form. For 2PY.U, 2PY.T and 2PY.1MU the measured wobble:Watson-Crick:sugar-edge isomer ratios are in good agreement with the calculated ratios, based on the ab initio dissociation energies and gas-phase statistical mechanics. The Watson-Crick and wobble isomers are thereby determined to be several kcal/mol less strongly bound than the sugar-edge isomers. The 36 observed intermolecular frequencies of the nine different H-bonded isomers give detailed insight into the intermolecular force field.

Spectroscopic Studies of Diatomic Gallium Halides

An extensive study of the available spectroscopic information on four gallium monohalides has been conducted. The literature survey extends to early 2003 and the experimental and theoretical data on the molecular constants for the ground state, as well as for the excited states of these molecules, is presented. A brief discussion on the spectroscopic properties of different electronic states, ionization potentials, ground state dissociation energies, and percentage ionic character are given. The Rydberg–Klein–Rees potentials for the electronic states and centrifugal distortion constants for the observed vibrational levels for the electronic states of GaX (X=F, Cl, Br, and I) are also presented.

Spectroscopic investigations on cometary molecules CO +, CH and CH +

The experimental potential energy curves for the electronic ground states of molecules like CO +, CH and CH + observed in comets are constructed by using the Rydberg–Klein–Rees method as modified by Vanderslice et al. The ground state dissociation energies are determined by curve fitting technique using the five parameter Hulburt–Hirschfelder (H–H) function. The estimated dissociation energies are 8.33±0.19, 3.48±0.903 and 3.89±0.102 eV for CO +, CH and CH +, respectively. These values are in good agreement with the literature values. Estimated dissociation energies of CO +, CH and CH + are used in the relation given by Gaydon and ionization potentials are evaluated for CO and CH molecules. The estimated ionization potentials are 14.03 and 10.85 eV , respectively for CO and CH. The Franck–Condon factors and r-centroids for the band system of A 2 Π – X 2 Σ + of CO + molecule have been calculated employing an approximate analytical methods of Jarmain and Fraser. The absence of the bands in this system is explained.

Estimation of potential energy curves, dissociation energies, franck-condon factors and r-centroids of comet interesting molecules

The experimental potential energy curves for the different electronic states of molecules like CN, CO and CS observed in comets are constructed by using the Rydberg-Klein-Rees method as modified by Vanderslice et al. The ground state dissociation energies are determined by curve fitting technique using the five parameter Hulburt-Hirschfelder (H-H)function. The estimated dissociation energies are 7.63 ± 0.187, 10.95 ±0.224 and 7.27 ± 0.152 eV for CN, CO and CS respectively. These values are in good agreement with the literature values. Estimated dissociation energies of CN, CO and CS are used in the relation given by Gaydon and ionization potentials are evaluated for CO and CS molecules. The estimated ionization potentials are 13.92and 12.15 eV for CO and CS molecules respectively. The r-centroids and Franck-Condon factors (FC Factors) for the band system of a 3Πr – X1Σ+ (a – X) and A1Π – X 1Σ+ (A -X) of CN, A 2Πi – X2Σ+ (A – X) and B2Σ+-X2Σ+ (B – X) of CO and a 3Πr – X1Σ+ (a – X) of CS molecules have been calculated employing an approximate analytical methods of Jarmain and Fraser and Nicholls and Jarmain. The absence of the bands in these systems are explained.

Ground-state potential of the Ca dimer from Fourier-transform spectroscopy

The B 1 Σ + u →X 1 Σ + g system in 4 0 Ca 2 was studied by Fourier-transform spectroscopy. Transitions to 730 ground-state levels were induced by the blue-green lines of an Ar + radiation and the single-mode radiation of a frequency-doubled continuous-wave Nd:YAG yttrium aluminum garnet laser. An accurate potential-energy curve, which covers 99.8% of the well depth, was derived directly from the experimentally observed differences between ground-state levels. Long-range analysis led to a revised value of the ground-state dissociation energy, 1102.08(9) cm - 1 , which differs by more than 7 cm - 1 from the previous experimental determination [C. R. Vidal, J. Chem. Phys. 72, 1864 (1980)]. A first estimate of the s-wave scattering length is reported.

Two new symmetry-adapted perturbation theories for the calculation of intermolecular interaction energies

We outline two new symmetry-adapted perturbation theories (SAPTs) and present some results obtained with them. The first is superior to the symmetrized Rayleigh–Schrodinger (SRS) theory in that it corrects a fundamental defect of that theory, namely, that carried to infinite order the SRS theory cannot predict even the ground-state energy for most interacting atoms and molecules. The new theory includes correction terms which have a large cumulative effect, but which, order by order, make only small contributions. When applied to interacting closed-shell systems and truncated after first order in the wave function, it is equal in accuracy to the SRS theory. Thus, it provides both an understanding of why the SRS theory gives results of useful accuracy and justification for its continued use when truncated to low order. The second new SAPT also corrects the SRS theory's flaw, but achieves significantly greater accuracy than the SRS theory when truncated after first order in the wave function. Applied to the interaction between the open-shell Li and H atoms, a critical test case, the second theory gives the ground-state dissociation energy with an error of 1%, whereas the SRS theory is in error by 38%. The LiH molecule is a critical test case because its physical ground-state energy, like that of nearly all systems, lies in a continuum of accessible states which violate the Pauli exclusion principle.

Photoinduced dissociation of methylnitrite on Ag( [formula omitted

Electronic excitations and photoinduced electron attachment states of methylnitrite (CH 3ONO) adsorbed on Ag(1 1 1) are investigated by ab initio methods. The calculated ground state energies of the cis and trans isomers of the methylnitrite molecule are nearly degenerate, with the trans structure lower than the cis by 0.03 eV at the CI level. Experimentally, the cis isomer is estimated to be more stable by 0.03 eV. The energy of methylnitrite in its ground electronic state on the silver surface is nearly the same for both isomer configurations and changes only slightly with isomer orientation and adsorption site. In both cis and trans forms, structures in which the internal oxygen points towards the surface and the O(internal)N internuclear axis lies between 30° and 45° from the surface are favored. The calculated adsorption energy is 0.60 eV for the cis isomer. Ground and excited state potential energy curves for dissociation to CH 3O/Ag and NO (gas phase) are calculated at the CI level for both internal electronic excitations and for electron attachment excited states. The calculated ground state dissociation energy is 1.5 eV, a value 0.20 eV less than calculated for the gas phase dissociation. The metal-mediated excitation (electron attachment to the adsorbate and hole in the metal) leads to a repulsive triplet state with a vertical excitation energy of 4.7 eV and negligible singlet–triplet splitting. A second excited state produced by electron excitation within methylnitrite produces distinct singlet and triplet states. The vertical excitation occurs at 2.4 eV for the triplet state and at 3.4 eV for the singlet state. In comparing the methylnitrite/Ag(1 1 1) potential energy surface to that of gas phase methylnitrite, a shallow minimum in the first excited singlet state for the molecule appears only as a plateau in the adsorbate/metal system when the excitation is from within methylnitrite. There is a 10-fold increase in methylnitrite/silver mixing in the metal-mediated excitation as compared to the internal excitation, which may explain the surprising experimental result that dissociation does not follow metal-mediated excitation.