Diatomic Interhalogens Research Articles

Is σ-hole an electronic exchange channel in YX⋯CO interactions?

A theoretical study of linear YX⋯CO complexes (in which YX are diatomic interhalogens or hydrogen halide) has been performed to high-level quantum chemical calculations. Calculations show that at the equilibrium geometry, the stabilizing effect that arises from the Pauli exclusion principle is more important than the electrostatic interactions. In addition, the stabilizing terms of the LMOEDA scheme increase with the σ-hole magnitude, being the exchange term the most affected one, followed by electrostatics, polarization and dispersion components. The PAEM function measured on the X⋯C interatomic interaction line gives a measure of the covalence of these interactions.

Surprising behaviors in the temperature dependent kinetics of diatomic interhalogens with anions and cations.

Rate constants and product branching fractions of reactions between diatomic interhalogens (ICl, ClF) and a series of anions (Br-, I-) and cations (Ar+, N2+) are measured using a selected ion flow tube apparatus and reported over the temperature range 200-500 K. The efficiency of both anion reactions with ICl is 2%-3% at 300 K to yield Cl-, increasing with temperature in a manner consistent with the small endothermicities of the reactions. The anion reactions with ClF are 10%-20% efficient at 300 K to yield Cl- and also show a positive temperature dependence despite being highly exothermic. The stationary points along the anion + ClF reaction coordinates were calculated using density functional theory, showing no endothermic barriers inhibiting reaction. The observed temperature dependence can be rationalized by a decreasing dipole attraction with increasing rotational energy, but confirmation requires trajectory calculations of the systems. All four cation reactions are fairly efficient at 300 K with small positive temperature dependences, despite large exothermicities to charge transfer. Three of the four reactions proceed exclusively by dissociative charge transfer to yield Cl+. The N2+ + ClF reaction proceeds by both non-dissociative and dissociative charge transfer, with the non-dissociative channel surprisingly increasing with increasing temperature. The origins of these behaviors are not clear and are discussed within the framework of charge-transfer reactions.

Reaction of 4-hydroxycoumarin or its O-substituted derivatives with diatomic interhalogens: ICl and IBr

ABSTRACTHerein, we present some aspects regarding the iodination/bromination of 4-hydroxycoumarin or its O-methyl or O-acetyl derivatives with iodine monochloride or iodine monobromide as halogenation reagents. Also, the investigation of photochemical transformation of the three 3-iodocoumarins was investigated for the first time.

Ab initio potential energy curves of the valence, Rydberg, and ion-pair states of iodine monochloride, ICl.

We present for the first time a coherent ab initio study of 39 states of valence, Rydberg, and ion-pair character of the diatomic interhalogen ICl species through large scale multireference variational methods including spin-orbit effects coupled with quantitative basis sets. Various avoided crossings are responsible for a non-adiabatic behaviour creating a wonderful vista for its theoretical description. Our molecular constants are compared with all available experimental data with the aim to assist experimentalists especially in the high energy regime of up to ~95,000 cm(-1).

Accurate first principles calculations on chlorine fluoride ClF and its ions ClF±

The present work focuses on the first (lightest) of the six diatomic interhalogens, namely ClF and its ions ClF+ and ClF-, in an effort to better understand these interesting species. Toward this end, we have performed highly correlated all electron ab initio calculations of multireference (MRCI) and single-reference coupled-cluster calculations, employing quintuple and sextuple correlation consistent basis sets. Within the K - S ansatz, we have examined all 12 states of ClF correlating adiabatically with the first energy channel, all 23 states of ClF+ correlating with the first three channels, and three states out of four of ClF- correlating with the first two channels Cl- + F and Cl + F-. Full potential energy curves at the MRCI/quintuple zeta level have been constructed for 12, 21, and 3 states of ClF, ClF+, and ClF-, respectively. After correcting for core–subvalence and scalar relativistic effects, albeit small as expected, and spin–orbit interactions, most of our results are in excellent agreement with available experimental data. Some lingering questions have been definitely settled. Our final recommended binding energies (D0 in kcal/mol) and equilibrium bond distances (re in A ) for \( C1F\,\left( {X^1 \Sigma^+} \right),\,C1F^+ \,\left({X^2 \Pi } \right),\,and\,C1F^- \left({X^2 \Sigma^+} \right) \) are [60.35, 1.6284], [67.40, 1.5357], and [29.80, 2.151], respectively. The adiabatic electron affinity of ClF, \( C1F,\,C1F\left({X^1 \Sigma^+} \right) + e^- \to C1F^- \left({X^2 \Sigma^+} \right) \), is \( EA_{ad} = 2.25 \pm 0.001 \) eV about 0.6 eV smaller than the suggested experimental value which is certainly wrong.

Energetics and Interactions of Mixed Halogen Adsorbates on the Si(100) Surface

The energetics of various ordered structures of the Si(100) surface with a 1:1 mixture of two adsorbates (hydrogen–halogen) or (two halogens) are investigated using ab initio density functional theory (DFT) calculations. Through an analysis of the calculated energies of various ordered adsorbate structures, the nearest-neighbor and next-nearest-neighbor interactions between halogen adsorbates are unveiled and observed to fit well with a proposed electron-cloud overlap model. Systematic trends are revealed: The mixing energy of two adsorbates favors desegregated structures. A (2 × 2) structure has the lowest energy on the rectangular Si(100) dimerized surface for all mixed adsorbate systems resulting from the stoichiometric adsorption of diatomic interhalogen molecules and hydrogen halides. These results are in good agreement with the scanning-tunneling microcopy (STM) observations on Si(100) after the adsorption of chlorine-contained molecules HCl and ICl but not for HBr and IBr.

Adsorption of Diatomic Interhalogens on the Si(100) and Ge(100) Surfaces

This work investigates the adsorption of diatomic interhalogens (XY = ICl and IBr) and hydrogen halides (HX = HBr and HCl) on Si(100) and Ge(100) surfaces by synchrotron radiation core-level photoemission and scanning tunneling microscopy (STM). It was found that mixed adsorbates (X and Y) or (H and X) each terminate a surface dangling bond while preserving the dimer structure. The coverage ratios of Cl/I and Br/I are slightly below the stoichiometric value of 1 for Si(100):ICl (the ICl-passivated Si(100) surface) and Si(100):IBr, respectively, but ∼1.4 for Ge(100):ICl. The X/H coverage ratios for HCl and Si(100):HBr are also less than 1. The mixed adsorbate system form well-ordered or partially ordered structures for chlorine-contained molecules on Si(100), but no adsorbate ordering is observed for bromide-contained molecules. In a sequel paper, we will present ab initio calculations for the energetics for the Si(100) surface with two mixed adsorbates to provide a more in-depth understanding of the experimental findings presented here.

Conformational study on the structures and energies of the weakly bound complexes of AlCl3 with diatomic molecules

AbstractIn this work we present the results of high level ab initio calculations on weakly bound complexes of aluminium trichloride and hydrogen halides, HX, halogens, X2 and diatomic interhalogens, XY (where X, Y = F, Cl, Br). Based upon these calculations we have predicted that all structures in the staggered conformation (except for Cl3AlFH and Cl3AlClH) are stable minima while those in the eclipsed configurations are transition state structures. In the XH complexes the strength of interaction with the Cl3Al group is FH > ClH > BrH. In the case of X2 species it is Br2 > F2 > Cl2, and finally in the XY (YX) group it is: FBr > ClBr > FCl > BrCl > BrF > ClF.

Conformational preferences of the structures, and energetics of the molecular complexes of boron trifluoride with some hydrogen halides, halogens and interhalogens

The optimized structures and interaction energies of a number of complexes of boron trifluoride, as electron acceptor, with some halogen bases, as electron donors, have been determined by means of ab initio molecular orbital calculations. The bases include the hydrogen halides (HF, HCl and HBr), the halogens (F 2, Cl 2 and Br 2), and the diatomic interhalogens (ClF, BrF and BrCl). In each case the major interaction takes place through a halogen atom of the base and the boron atom of BF 3. In the complexes with the hydrogen halides the preferred conformation is the eclipsed species, while for the other two series the staggered conformer is usually more stable. The strengths of interaction correlate with some of the properties of the bases, such as the gas phase basicities, the ionization energies, the polarizabilities, and the dipole and quadrupole moments, where appropriate.

HFI and DFT study of the bonding in complexes of halogen and interhalogen diatomics with Lewis base

We have analyzed by means of DFT calculations with use of the pseudo-potential the nuclear quadrupole coupling constants of a range of XY⋯B complexes (n aσ type in Mulliken notation) formed between diatomic interhalogen molecules XY and Lewis bases B. The geometrical parameters, rotational and halogen nuclear quadrupole coupling constants obtained by these calculations substantially corresponded to the data of microwave spectroscopy in the gas phase. An analysis of the quality of the calculations that employ the pseudo-potential and the expanded basis set for the halogen compounds was carried out. The ZORA model is shown to be a viable alternative to the computationally demanding BH and HLYP model for the calculation of halogen and nitrogen coupling constants in molecules. In addition, the ZORA model, in contrast to the pseudo-potential model, leads to realistic values of iodine nuclear quadrupole coupling constants. From electron partitioning analyses and Klopman's approach it follows that for the ICl⋯B complexes the electrostatic bonding is predominant relative to covalent bonding.

Mean Amplitudes of Vibration of the Halogen Molecules

Mean amplitudes of vibration of the halogen molecules F2, Cl2, Br2, and I2 have been calculated from known spectroscopic data in the temperature range between 0 and 1000 K. The results are briefly discussed, and some comparisons with the results of the related diatomic interhalogen molecules, as well as with experimental values obtained by electron diffraction experiments, are made.

Relativistic effects at the correlated level. An application to interhalogens

Relativistic effects are significantly important in understanding the electronic structure and spectra of heavy atoms or molecules containing such atoms. Estimation of relativistic effects at the coupled-cluster (CC) level, using the Cowan—Griffin quasi-relativistic many-electron Hamiltonian, is described. The relativistic effects are treated as an external perturbation to the non-relativistic Born—Oppenheimer many-electron Hamiltonian and are evaluated analytically by the “relaxed” density formulation of coupled-cluster (CC) theory. Applicability of the method is demonstrated by calculating relativistic corrections to the ground state energies and dipole moments of diatomic interhalogens. We also present comparisons with relativistic effective potential results.

Electric properties of diatomic interhalogens. A study of the electron correlation and relativistic contributions

The recently developed polarized basis sets for halogen atoms are used to calculate several basic electric properties of diatomic interhalogen molecules. In the valence approximation the electron correlation contribution is treated at the level of the fourth-order many-body perturbation theory approximation. The corresponding results are corrected for the core-polarization and relativistic effects. It is shown that the dipole moments of heavy interhalogen diatomics are considerably affected by the relativistic contribution, while the core-polarization effects are of lesser importance. The calculated, relativistically corrected, dipole moments are in agreement with experimental data and are used to discuss the reliability of the effective core potential approximation. The calculated quadrupole moments and parallel components of the dipole polarizability tensor are only marginally affected by contributions due to core-polarization and relativistic terms. The geometry derivatives of dipole moments and dipole polarizabilities computed in this study can be used for the evaluation of intensities in infrared and Raman spectra of interhalogen diatomics.

Non-empirical valence-electron calculations on the diatomic halogens and interhalogens

The non-empirical valence–electron (NEVE) method for molecular orbital calculations on molecules containing heavy atoms has been extended to include fourth-row atoms in a minimum STO basis calculation. Calculations on the halogens F2, Cl2, Br2 and I2, and the diatomic interhalogens CIF, BrF, BrCl, IF, ICl and IBr give results which are comparable with those of available ab initio calculations. Calculation of the Koopmans' defect for these molecules shows that the defect is only significant for the fluorine-containing molecules, and that the resulting orbital sequence agrees with the experimental photoelectron spectroscopic data in all cases. Calculated spin-orbit splittings also correlate with the observed values.

Diatomic interhalogens: Systematics and implications of spectroscopic interatomic potentials and curve crossings

Spectroscopically derived potential curves for the low-lying excited states of the homonuclear and heteronuclear diatomic interhalogens are systematized by taking cognizance of the spin-orbit state of the dissociation products. Observed regularities lead to the prediction of a bound B (3Π0+) state of F2 with r′e ≃ 1.9 Å, D′e ≃ 3300 cm−1. Several of the heteronuclear interhalogens show evidence of a strong interaction between the B (3Π0+) state and a repulsive Y (O+) state, leading to the formation of a new B′(O+) state. An analysis of these interactions has led to the construction of sets of diabatic potentials consistent with the best estimated adiabatic curves and thus to the determination of the crossing points rx and interaction strengths V12(rx). The patterns of V12(rx) values suggest that they depend mainly upon the spin-orbit coupling constant of the excited atomic dissociation product. Reported also are repulsive segments of potential curves deduced for the Y (O+) states for a series of 1Π states and a few higher-lying (Z) states, the latter two series from analysis of existing continuum absorption data. Repulsive interactions in all four families of states studied [3Π0+, 1Π1, Y(O+), and Z] show clear regularities governed by steric effects. Implications of the present results with respect to the theory of interatomic forces, predissociation phenomena, and the scattering of ground state halogen atoms are discussed.

Selected valence electron split‐shell molecular orbital calculations on the diatomic interhalogen molecules

AbstractSelected valence electron split‐shell molecular orbital calculations have been performed on the diatomic interhalogen molecules in order to obtain their binding energies, equilibrium internuclear distances, vibrational force constants, dipole moments and nuclear quadrupole coupling constants. The results are compared with the corresponding closedshell values and with those of some previous semiempirical and nonempirical all valence electron calculations. It is observed that the selected valence electron split‐shell molecular orbital method which involves the least amount of computations yields results in better agreement with experiment than other methods.

The helium-(I) photoelectron spectra of some halogens and diatomic interhalogens

Medium resolution helium(I) photoelectron spectra of the halogen molecules Cl 2, Br 2 and I 2, and of the diatomic interhalogens, ICl and IBr, are reported. Vibrational fine structure is discernible in the first photoionisation bands of Cl 2, Br 2 and ICl, while multiplet splittings are evident in the photoelectron spectra of Br 2, I 2, ICl and IBr. The details of the spectra are consistent with established qualitative concepts of molecular orbital theory.

THE ELECTRONIC EMISSION SPECTRUM AND MOLECULAR CONSTANTS OF IODINE MONOFLUORIDE

Observation by the author (Durie 1951) of a well-developed band system in the emission from an iodine–fluorine flame provided the first evidence for the existence of iodine monofluoride (IF), the last of the six possible diatomic inter-halogen compounds to be detected. The spectrum, which lies in the region 4 300 to 7 600 Å, has since been photographed under high resolution using a 21-ft concave grating spectrograph. The rotational structure of the bands is shown to be consistent with an A3Π0+ → X1Σ transition in the IF molecule. A rotational and vibrational analysis of the bands has been carried out and the molecular constants evaluated for IF. The results are as follows:[Formula: see text]The present evidence relating to the value of the dissociation energy of IF is discussed.

High-resolution Raman spectroscopy in the red and near infrared—II: Vibrational frequencies and molecular interactions of halogens and diatomic interhalogens

The Raman frequencies of a series of diatomic halogen and interhalogen molecules in the liquid state and in different solvents are reported. The measurements were carried out on spectra excited in the red and near-infrared spectral range by helium or rubidium radiations, and photographed under high or medium dispersion. The results are tabulated together with the values Δ G 1 2 as obtained from band spectra for the isolated molecules and with available data from infrared absorption measurements and from simultaneous transitions. In comparison to the frequencies to be expected for the non-associated molecules, the observed values show a marked decrease, due to interactions between identical molecular species, or to solute-solvent interactions. Interactions of the latter kind lead, in some cases, to the formation of loose charge-transfer complexes with the solvent acting as donor, and, consequently, to a more pronounced change of frequency of the accepting halogen. The origin of still larger effects, observed on solutions in pyridine, is discussed.

Mass spectra of halogen fluorides

Appearance potentials and positive-ion mass spectra were determined for IF 5, BrF 5, BrF 3 and ClF 3. A negative-ion study was made on BrF 3. The gas samples were subjected to rate of effusion studies in the mass spectrometer sample system and shown to contain diatomic halogen and halogen fluoride impurities. Halogen oxyfluorides were detected in BrF 5, BrF 3 and ClF 3 samples and reaction between O 2 and BrF 5 was observed on mixing. Upper limits for ionization potentials were obtained for IF 5, IF, ICl, IBr, BrF 3, BrF, BrCL, ClF 3 and ClF directly from appearance potentials. Ionization potentials for the radicals BrF 2 and ClF 2 were deduced using supplementary thermochemical data. Ionization potentials of diatomic interhalogens with the exception of BrCl give bond dissociation energies for interhalogen molecule ions approximately equal to corresponding values for neutral molecules.