Heteronuclear Diatomic Molecules Research Articles

The Asymptotic Behavior of the Site-Site Ornstein-Zernike Equation and RISM-2 Approximations for Polyatomic Molecular Fluids

It is shown that the asymptotic properties of the reference interaction site model (RISM)-2 type integral equations for polyatomic molecular fluids are quite similar to those of simple fluids. The exact asymptotic form of the new site-site direct correlation function C αγ ( r ), which is defined by the site-site Ornstein-Zernike equation, is given by using the exact asymptotic form of the site-site total correlation function. The result is C αγ ( r )≃- U (1, 2)/ k B T for nonpolar fluids composed of homonuclear diatomic molecules as well as heteronuclear diatomic molecules, where U (1, 2) is an intermolecular potential, k B the Boltzmann constant and T the absolute temperature. The asymptotic form of C αγ ( r ) given by the RISM-2 approximations is found to be in accordance with the exact result. Thus, the RISM-2 theory is concluded to have no theoretical inconsistency like that in the RISM-1 theory.

Production and characterization of some mixed Group V A dimers in solid neon

Vaporization of ternary III–V mixtures is shown to provide a convenient source of the Group V heteronuclear diatomic molecules. Several such mixtures were vaporized and the vapors condensed in neon matrix and examined by time resolved, laser induced fluorescence spectroscopy. The excitation spectra of AsP and SbP dimers were examined and several new excited electronic transitions were observed and analyzed. The assignment of the new states is discussed and the electronic structure of these molecules reviewed and summarized.

Generalized 1/Z expansion for heteronuclear molecules

AbstractWe have first studied empirical regularities in various series of heteronuclear diatomic molecules between the energy E, the total number of electrons N, the equilibrium distance Re and Z̄ = (Z1Z2)1/2 where Z1e and Z2e are the nuclear charges in the diatom. In particular, for various alkali halide series, Re2|E|/N5/3 is shown to correlate rather simply with Z̄Re3. Some theoretical basis is afforded by generalizing the 1/Z expansion used early by the writers in work on homonuclear diatomics. Finally, when Z2/Z1 → ∞, a model is presented which predicts a finite asymptotic bond length and this prediction is confronted with available experimental data for both heteronuclear diatoms and for the polyatomic series CH4 to SnH4.

Dissociation energies of diatomic molecules related to equilibrium bond lengths

The problem of calculating dissociation energies of all but the lightest molecules remains a formidable one in quantum chemistry. However, the calculation of equilibrium internuclear distances is much simpler. Therefore, in this paper, we have explored whether the dissociation energies of diatomic molecules can be directly related to the nuclear–nuclear potential energy Vnn, plus molecular invariants. These latter quantities are the total number of electrons N and the ‘‘approximate’’ invariant, the total kinetic energy of the separated atoms, denoted by T. For chemically similar series, a marked correlation of D with Vnn/T is demonstrated, which for the N2, P2, etc. series can be represented approximately by D/N1/2=[300(Vnn/T)−6] kcal which would mean no binding above a limiting atomic number, lying higher, however, than those that span the Periodic Table. The existence of a minimum value of Vnn/T in groups of chemically stable homonuclear diatomic molecules is then contrasted with the situation in chemically similar series of heteronuclear diatomic molecules. Here, no minimum value of Vnn/T is found, due, it is argued, to the stabilization of these molecules by charge transfer.

Theoretical electronic state and angular resolved kinetic energy distributions of sputtered diatomic molecules

Electronic state selected translational kinetic energy and polar angular distributions of several homonuclear and heteronuclear diatomic molecules, corresponding to direct ejection and recombination mechanisms of sputtering, are presented. The initial atom separation on, and axis orientation to, the surface are only weakly reflected in the distributions, in contrast to the atomic cascade properties and ejection mechanism. Many observed features of kinetic energy distributions can be reproduced by the simulation, including additional peaks previously interpreted as due to thermal or other processes. Measurements of polar angular distributions are shown to contain important information on atom-pair momentum correlations in collision cascades.

Electronic structure of some heteronuclear diatomic molecules in the local spin density approximation

Ab initio self-consistent spin polarized calculations have been performed for the electronic structure of the heteronuclear diatomic molecules LiH, CO, and NO; using local spin density functional theory. The Kohn–Sham functions have been expanded in terms of a basis set of Gaussian orbitals. All the one and two electron integrals are calculated exactly. The matrix elements of the exchange correlation potential are computed numerically using a two dimensional doubling grid developed for this purpose. The total energy, the binding energy, the equilibrium distance, the vibrational frequency, and the dipole moment are reported and compared with experimental results and with other calculations. The agreement of our results with experimental values is very good in all cases.

Stark effect, polarizabilities and the electric dipole moment of heteronuclear diatomic molecules in 1Σ states

The theory of second-order Stark effect in 1Σ states of heteronuclear diatomic molecules is thoroughly reviewed. The rigorous treatment given demonstrates that by introducing rotational, vibrational and electronic branch polarizabilities, the intrinsic character of the second-order Stark effect in diatomic molecules can be shown to be related more closely to polarizabilities than to dipole moments. The well-known expression for the Stark shift in 1Σ levels which is dominated by the square of the dipole moment is only a crude, though sufficient approximation whenever large dipole moments are involved. For small dipole moments, however, this approximation is likely to fail, leading to an erroneous determination of such dipole moments. In the limiting case of negligible influence of the molecular rotation on the vibronic matrix elements, the arithmetic mean of the electronic branch polarizabilities turns out to be equal to the well-known static electronic polarizabilities α ∥ and α ⊥. The results are applied to the interpretation of the Stark splitting in the A 1Σ +, υ′ = 5, J′ = 1 level of 7LiH, recently determined by Stark quantum-beat spectroscopy.

Rate Data for Inelastic Collision Processes in the Diatomic Halogen Molecules

A detailed compilation of rate data for inelastic collision processes involving the homonuclear and heteronuclear diatomic halogen molecules is presented. The literature has been surveyed through April 1983. Processes that are considered include exchange of energy between electronic, vibrational, rotational and translational degrees of freedom, electronic quenching, dephasing, depolarization, pressure broadening, and spontaneous radiation. Collision partners include rare-gas atoms, halogen and other diatomic molecules, and polyatomic species; a few measurements in liquids and cryogenic matrices are also included. Each data entry includes collision partner, temperature, method of measurement, and an error estimate where available. While a large mass of data is available for these systems, there still exist sizable gaps in our knowledge concerning these processes, particularly for the interhalogen species.

A theoretical approach to rotationally inelastic scattering of a heteropolar rigid rotor by rigid and flat surfaces

Rotationally inelastic scattering of a rigid rotor, which represents a heteronuclear diatomic molecule, by rigid and flat solid surfaces is investigated by assuming three types of potential. It is demonstrated that the observed Boltzmann-like profile for low excitations in the NO-Ag(111) scattering experiment may be ascribed to the first of the two rotational rainbow peaks. It is also shown that “quasi-trapping” of molecules occurs if the potential has an attractive part.

Optically pumped gas laser using electronic transitions in the NaRb molecule

Laser superradiance was achieved for the first time as a result of an electronic transition in a diatomic heteronuclear molecule as a result of direct optical pumping. This superradiance was observed in the region of 670 nm due to a transition to the ground stated X 1Σ + of the intermetallic alkali molecule NaRb pumped by radiation from a pulsed copper vapor laser (λ =510.6 nm).

Density functional theory of asymptotic form of electron density in heteronuclear diatomic molecules

Density functional theory is shown to lead to a simple differential equation for the asymptotic form of the electron density in a diatomic molecule. This equation can be solved, if one assumes building blocks which in a heteronuclear diatomic molecule correspond to fractionally charged ions. The resulting expression for the asymptotic electron density can be approximately expressed in terms of the fractional charge and the chemical potentials of the two free atoms. Two models are proposed for estimating the fractional charge.

The 〈110〉 oriented FCl− molecule–ion in KFa)

The heteronuclear diatomic molecule–ion FC1− with its molecular axis oriented along a crystal face diagonal, i.e., FC1− 〈110〉, has been produced by ionizing radiation in single crystal KF doped with PbCl2 and KC1. Evidence to support this species identification as well as its orientation relative to the lattice is obtained from anisotropic optical absorption spectral measurements as well as from electron spin resonance (ESR) absorption spectra. Optical absorption spectral data, estimates of the molecular reorientation temperature, as well as ESR absorption spectral parameters are given for the FCl− 〈110〉. A qualitative explanation of the differences of the optical and ESR parameters of FCl− 〈111〉 and FCl− 〈110〉 is discussed.

Zero-core-contribution calculation of photodetachment characteristics of heteronuclear diatomic anions

The zero-core-contribution method is extended to study the photodetachment of heteronuclear diatomic molecules. Total photodetachment cross sections are calculated for the ions O${\mathrm{H}}^{\ensuremath{-}}$, S${\mathrm{H}}^{\ensuremath{-}}$, and Se${\mathrm{H}}^{\ensuremath{-}}$. The anisotropy factor $\ensuremath{\beta}$ is also calculated for O${\mathrm{H}}^{\ensuremath{-}}$. The agreement with measured values of these quantities is good.

Nuclear–nuclear potential energy related to total number of electrons in light molecules

Using self-consistent field calculations for a wide variety of molecules having total number of electrons N, with 10≤N≤32, the nuclear–nuclear potential energy for equilibrium geometry is studied as a function of Δ/ ‖ E ‖, where Δ is defined as E−3/2 Es, with E and Es the ground-state energy and the sum of orbital energies, respectively. The plots for the molecules considered, in the range 10≤N≤22 are accurately represented by Vnn=0.12N2+68 Δ/ ‖ E ‖ a.u. Thus, we can define a series of ‘‘canonical’’ molecules with Δ/E=0, in which Vnn is solely determined by the total number of electrons. Canonical heteronuclear diatomic molecules with nuclear charges Z1 and Z2 have then equilibrium bond lengths given by Re−1=0.12(1+ε)2/ε with ε=Z2/Z1, which for homonuclear molecules gives Re=1.10 Å, near to the value for N2. Empirically, N2 lies at the minimum of the bond length vs N curve for the homonuclear molecules excluding H2. We know of no canonical heteronuclear diatomic molecules, but, nevertheless, two diatomic hydride series obey the canonical type of relationship with a substantially modified constant.

Vibration-rotational and rotational intensities for CO isotopes

Dipole moment matrix elements have been computed for the five most abundant isotopes of CO. The wave functions utilized were obtained from a direct solution of the Schrödinger equation with an accurate RKR potential. The dipole moment function, in the form of a Padé approximant, was chosen to reproduce the experimental measurements near equilibrium, to have the proper united and separated atom limits, and to have the correct long-range asymptotic functional dependence on internuclear separation. Because of the large number of transitions involved, and to facilitate applications, the squares of the dipole moment matrix elements were fitted by a least-squares procedure to polynomials in v and J. Predictions for the 5-0 and 6-0 rotationless matrix elements and Herman-Wallis coefficients are given, and their dependence on the isotopic reduced mass is discussed. For the pure rotational band, v = v′ = 0, explicit Einstein A values and transition frequencies were calculated for the three most abundant isotopes for J up to 55. The corresponding dipole moment matrix elements were also fitted to simple polynomials in m and the dependence of the coefficients on the reduced mass given. The present results incorporate the most accurate and extensive intensity measurements and theoretical dipole moment function data for any heteronuclear diatomic molecule. In view of this, because of the importance of the CO laser, the accuracy of the spectral frequencies, and the ubiquity of the CO molecule, it is reasonable to expect that some of these lines, in particular, in the fundamental band of 12C 16O, can serve as laboratory standards for intensity measurements.

Prediction of vibrational constants for gas-phase heteronuclear diatomics and atoms adsorbed on surfaces

An empirical relationship is presented for predicting vibrational constants for gas-phase heteronuclear diatomic molecules and atoms adsorbed on surfaces. Excellent agreement with experimental values is obtained. The method is used for predicting the unknown vibrational constants of AgS and CTe.

Semiclassical vibrational spectra for diatomic molecules: Application to HF, CO, and NO

Semiclassical dipole-moment matrix elements are calculated for HF, CO, and NO using realistic dipole-moment functions, and are in excellent agreement with those calculated from quantum mechanics. The first two cases have the Δn=1 vibrational transition exhibiting a maximum at excited vibrational states and then becoming nearly forbidden at higher vibrational states; in this region, the Δn=2 transition becomes more probable than the Δn=1 transition. This behavior is also expected for NO or for any heteronuclear diatomic molecule whose dipole moment has a maximum at an internuclear distance greater than re.

Dipole moments, molecular ionization potentials, and asymptotic form of electron density in hydrogen halides and other heteronuclear diatomic molecules

From available experimental data, it is demonstrated that the electric dipole moments of hydrogen halides and other heteronuclear diatomic molecules are strongly correlated with molecular ionization potentials. By means of the Euler equation of density functional theory, solved far from nuclei, it is shown that the asymptotic form of the electron density is determined by the spherically averaged density and by the ratio dipole moment to ionization potential.

Physical adsorption of a heteronuclear diatomic molecule onto a solid surface: a theoretical approach

A theoretical study is made of the physical adsorption of the heteronuclear diatomic molecule H 35Cl on a solid crystalline argon surface. The potential energy of interaction between the adsorbate molecule and adsorbent is computed by a lattice summation over the requisite number of individual HCl...Ar “pair” interactions, described using an equation developed by Neilson and Gordon. Adsorption is considered at four sites on the (111) face of the argon cubic close-packed lattice: the tetrahedral (T) hole, the octahedral (O) hole, above a surface atom (A); and the saddle point (SP). Values of the potential energy are evaluated as a function of location and orientation of the adsorbate relative to the adsorbent surface. The results indicate that adsorption is preferred at the T and O sites and that the adsorbate can be considered localized at temperatures < 30 K. The preferred molecular orientation for adsorption at a T or O site is perpendicular to the surface with the H end pointing downward while at an A site the molecule prefers an orientation parallel to the surface. The Schrödinger equation is solved for the rotational-librational energy levels of an adsorbed H 35Cl molecule above the tetrahedral hole of the argon surface. At temperatures below 10–15 K the adsorbate molecules can be considered confined to their ground rotational-librational energy states.

Dissociation Energy of the SbPb Moleculc from Mass Spectrometric High Temperature Studies

Abstract The observation of the gaseous BiPb molecule [1,2] suggests the existence of heteronuclear diatomic molecules of lead with the group V-b elements. The present paper reports on the identification of the SbPb(g) molecule and the determination of its dissociation energy by mass spectrometric Knudsen-effusion method.