Calculation of bond energies in diatomic molecules

Theoretical Chemistry Accounts - An extrapolation method is proposed for an approximative evaluation of covalent bonding powers of some elements from their electronegativity values. Using these...     

Observed adiabatic corrections to the born-oppenheimer approximation for diatomic molecules with ten valence electrons

Using millimeter-wave (mw) spectroscopy pure rotational transitions were measured with very high precision in several vibrational states for many compounds of the group III/VII and IV/VI diatomic molecules. The spectra were fitted to the usual Dunham expansion adopting the normal mass relations for the Y_lk except for Y₀₁ in order to combine all data of different isotopes for the same compound. For Y₀₁ the atomic mass relation given by Watson is used which introduces phenomenological parameters Δ₀₁^A, Δ₀₁^B for molecule AB taking the adiabatic and nonadiabatic corrections to the Born-Oppenheimer approximation into account. All observed spectra are well described by such a procedure. From these calculations the correction parameters Δ₀₁^A, Δ₀₁^B were obtained with an accuracy of ≈ 10% or better. Using known values of the rotational gJ factor and of the electric dipole moment the nonadiabatic part was calculated and with this result the adiabatic part was evaluated from Δ₀₁ for each atom. The adiabatic correction does not change very much for one specific atom by varying the chemical counterpart and in general it is less than 30% of the total correction for this class of molecules. The only exceptions are InI and the Tl and Pb compounds for which the adiabatic corrections are obtained ten to hundred times larger than those of the other compounds. No explanation is known for this behavior in the published literature.     

Analysis of adiabatic passage by light-induced potentials with chirped laser pulses in three- and four-level diatomic systems

This paper describes an investigation into the process of adiabatic passage by light-induced potentials (APLIP), which was previously suggested as a method for employing two strong picosecond laser pulses to transfer the population between two electronic states. We have extended earlier numerical studies in order to assess the feasibility of an experimental implementation of the APLIP concept. APLIP has been modeled in a three-level model system based on Na2 with chirped pulses, using laser parameters available from a typical chirped pulse amplified Ti:sapphire laser. The model showed that the APLIP process remains essentially unchanged for chirped pulses of equal magnitude and the opposite, or equal and positive sign of chirp as compared to the transform-limited case. We also examined the case of additional electronic states by introduction of a fourth state that lies close to the "target," i.e., final, state. The investigation showed that there are circumstances in which a significant fraction of the population gets transferred to this state which will disrupt the APLIP process. However, by switching to this fourth state as the target state in an experiment, good transfer efficiency is recovered. The results of the extension of the original APLIP modeling to chirped pulses and additional electronic states indicate that an APLIP experimental realization should be feasible in Na2.     

Calculation of bond dissociation energies of diatomic molecules using bond function basis sets with counterpoise corrections

Bond function basis sets combined with the counterpoise procedure are used to calculate the molecular dissociation energies D_e of 24 diatomic molecules and ions. The calculated values of D_e are compared to those without bond functions and/or counterpoise corrections. The equilibrium bond lengths r_e and harmonic frequencies o_e are also calculated for a few selected molecules. The calculations at the fourth-order Møller-Plesset approximation (MP 4) have consistently recovered about 95–99% of the experimental values for D_e; compared to as low as 75% without use of bond functions. The calculated values of r_e are typically 0.01 Å larger than the experimental values, and the calculated values of o_e are over 95% of the experimental values. © 1996 John Wiley & Sons, Inc.     

An analytic representation of the radial dependence of adiabatic and non-adiabatic corrections from molecular spectra of diatomic molecules

A method of determining the radial dependence of the adiabatic and non-adiabatic corrections contributing to the spectroscopie parameters Δ^a,b_kl of diatomic molecules according to an analytic representation is proposed. The method is applied to HCl and CO, and results for LiH are compared with published data.     

Electrophoretic manipulation of single DNA molecules in nanofabricated capillaries

We demonstrate the use of nanofabricated capillaries, integrated as part of a microfluidic structure, to study the electrophoretic behaviour of single, fluorescently-labelled, molecules of DNA as a function of capillary size. The nanocapillaries, fabricated using a focused ion beam, have cross-sections down to 150 x 180 nm. Control of single-molecule direction and velocity was achieved using voltage manipulation. DNA mobility was found to increase with decreasing cross-section, which we interpret in terms of reduced electro-osmotic counter-flow. Such nanofabricated capillaries as part of larger fluidic structures have great potential for biotechnology, particularly single molecule manipulation and analysis.     

MRD-CI potential surfaces using balanced basis sets. VI. Correlation of bond order with bond function composition for first-row diatomic molecules

This article presents theoretical calculations on bond energies for the first-row diatomics C₂, CN, CO, CF, N₂, NO, NF, O₂, FO, and F₂, which vary in bond order from one to three. The atomic-centered basis functions are systematically augmented with bond functions (BFs), which range in composition from (sp) to 2(spd), to determine the basis set which yields a dissociation energy closest to the experimental D_e. A strong correlation is found to exist between the bond order and the number of BFs required in the optimum basis set. Based on these results, we are able to predict the optimum composition of the BF basis which should be added to a DZP-quality AO basis set for a case in which only the bond order is known. These optimized BF basis sets are shown in the accompanying article to give more accurate potential curves than larger basis sets without bond functions.     

The collinear collision of two diatomic molecules. An application of the adiabatic approximation and the t- and k-matrix methods

We present a ‘partial decoupling“ scheme by which the collinear collision of two diatomics is reduced to an atom-diatomic collinear collision with new definitions for the parameters E, m, and a. The pseudo atom-diatomic problem is studied using the adiabatic approximation of Thiele and Katz and the first order distorted wave T- and K-matrix methods. We compare our results to the numerical results of Riley and Kuppermann and conclude that their results are reliable only for the transitions 00 → 01 and 01 → 10. We prepare a set of ‘corrected“ adiabatic transition probabilities and compare the approximate T- and K-matrix results to this set The accuracies of these approximate methods are then seen to be consistent with earlier conclusions concerning the application of the first order distorted wave approximation to atom-diatomic collinear collisions.     

Multiphoton ionization versus dissociation of diatomic molecules irradiated by an intense 40 ps laser pulse

The production of molecular and atomic ions has been measured for CO, N₂ and O₂ with 1064 and 532 nm 40 ps pulses in the 10¹²-10¹⁴ W cm^?2 intensity range. A simultaneous ionization-dissociation process occurs at lower intensities, while a sequential process appears in oxygen at higher intensities.     

Coherent population transfer in molecules coupled with a dissipative environment by intense ultrashort chirped pulse. II. A simple model

We have developed a simple and physically clear picture of adiabatic rapid passage (ARP) in molecules in solution by careful examination of all the conditions needed for ARP. The relaxation effects were considered in the framework of the Landau-Zener model for random crossing of levels. The model enables us to include into consideration non-Markovian Gaussian-correlated noise. It explains all the numerical results obtained in the first paper of the series [B. D. Fainberg and V. A. Gorbunov, J. Chem. Phys. 117, 7222 (2002)], in particular, that for positive chirp pulse excitation relaxation favors more efficient population transfer with respect to the relaxation-free system with frozen nuclear motion. We also relate parameters of non-Markovian Gaussian-correlated noise with irreversible dephasing time of an optical transition by calculating the photon echo signal attenuation.     

Ornstein-Uhlenbeck diffusion quantum Monte Carlo study on the bond lengths and harmonic frequencies of some first-row diatomic molecules

This article accesses the performance of the Ornstein-Uhlenbeck diffusion quantum Monte Carlo with regard to the calculation of molecular geometries and harmonic frequencies of H2, LiH, HF, Li2, LiF, CO, N2, and F2 molecules. A comparison of the results for the eight first-row diatomic molecules from experiments, CCSD(T)/6-311G(3df,3pd) and CCSD(T)/cc-pV5Z levels of theory as well as our work is given. The results presented show that quantum Monte Carlo is becoming powerful tools for ab initio electronic structure calculations.     

Measurement of the field-free alignment of diatomic molecules

An apparatus was constructed to experimentally quantify the field-free alignment of diatomic molecules irradiated by strong femtosecond laser pulses. In this apparatus, both homodyne and pure heterodyne detections were realized. The alignment signal is proportional to [ - 1/3](2) for homodyne detection and ( - 1/3) for pure heterodyne detection, where theta is the polar angle between the molecular axis and the laser polarization direction. Fourier transform spectra of the homodyne signal and the pure heterodyne signal were also studied. By comparing the alignment signal and its Fourier transform spectrum with the numerical calculation of the time-dependent Schr?dinger equation, we demonstrated that the pure heterodyne signal directly reproduced the alignment parameter , and its Fourier transform spectrum provided information regarding the populations of different J states in the rotational wavepacket.     

Squeezing the ground vibrational state of diatomic molecules

We study the squeezing of minimal width vibrational wave packets of diatomic molecules, like Na₂, by using several laser schemes that couple the ground and excited electronic configurations of the molecule. The different schemes imply diabatic and adiabatic laser transformations, or a combination of both, whose efficiency and required physical resources are compared and analyzed.     

Atomic polarization in the photodissociation of diatomic molecules

The angular momentum polarization of atomic photofragments provides a detailed insight into the dynamics of the photodissociation process. In this article, the origins of electronic angular momentum polarization are introduced and experimental and theoretical methods for the measurement or calculation of atomic orientation and alignment parameters described. Many diatomic photodissociation systems are surveyed, in order to provide an overview both of the historical development of the field and of the most state-of-the-art contemporary studies.     

On-site manipulation of single chromosomal DNA molecules by using optically driven microstructures

We report a novel method for manipulation of single giant DNA molecules under a video microscope. Using optically driven microstructures, we manipulated chromosomal DNA of length in the order of millimetres, extended by electroosmotic flow without DNA breakage in aqueous solution: we picked up DNA, using microfabricated hooks and wound it around microfabricated bobbins.     

Thermal expansivity of tetrahydrofuran clathrate hydrate with diatomic guest molecules

The guest dynamics and thermal behavior occurring in the cages of clathrate hydrates appear to be too complex to be clearly understood through various structural and spectroscopic approaches, even for the well-known structures of sI, sII, and sH. Neutron diffraction studies have recently been carried out to clarify the special role of guests in expanding the host water lattices and have contributed to revealing the influence factors on thermal expansivity. Through this letter we attempt to address three noteworthy features occurring in guest inclusion: (1) the effect of guest dimension on host water lattice expansion; (2) the effect of thermal history on host water lattice expansion; and (3) the effect of coherent/incoherent scattering cross sections on guest thermal patterns. The diatomic guests of H 2, D 2, N 2, and O 2 have been selected for study, and their size and mass dependence on the degree of lattice expansion have been examined, and four sII clathrate hydrates with tetrahydrofuran (THF) have been synthesized in order to determine their neutron powder diffraction patterns. After thermal cycling, the THF + H 2 clathrate hydrate is observed to exhibit an irreversible plastic deformation-like pattern, implying that the expanded lattices fail to recover the original state by contraction. The host-water cage dimension after degassing the guest molecules remains as it was expanded, and thus host-guest as well as guest-guest interactions will be altered if guest uptake reoccurs.