HI Molecule Research Articles

The adsorption of halogen molecules on Ti (110) surface

Adsorption of halogen on the metal surface has received much attention due to its technological applications and major relevance for material surface processing, corrosion protection and etching. In this work, first-principle approach was used to investigate the interaction of halogen molecules on Ti (110) surface. The present results revealed that adsorption of the halogen molecule is exothermic and occurs by dissociation bonding. The HF molecule was found to be more thermodynamically stable than the HI molecule. In addition, our results revealed that the adsorption of halogen ions on Ti (110) surface is energetically favourable than the adsorption of halogen molecule. The possible adsorption sites were tested, and the top site position was found to be the most favourable followed by the hollow and bridging site for both halogens. Furthermore, the results showed the linear relationship between adsorption energy strength and charge transfer. Also, the density of states and charge density difference was studied to investigate the electronic interaction. The charge redistribution showed an electron depletion on Ti atom and charge accumulation on the halogen region.

Calculation of the structure, potential energy surface, vibrational dynamics, and electric dipole properties for the Xe:HI van der Waals complex

We report the structure and spectroscopic characteristics for the Xe:HI van der Waals binary isomers determined from variational solutions of two-dimensional and three-dimensional (3D) vibrational Schrödinger equations. The solutions are based on a potential energy surface computed at the coupled-cluster level of theory including single and double excitations and a non-iterative perturbation treatment of triple excitations [CCSD(T)]. The dipole moment surface was calculated using quadratic configuration interaction (QCISD). The global potential minimum is shown to be located at the anti-hydrogen-bonded Xe-IH isomer, 21 cm(-1) below the secondary local minimum associated with the hydrogen-bonded Xe-HI isomeric form. The dissociation energy from the global minimum is 245.9 cm(-1). 3D Schrödinger equations are solved for the rotational quantum numbers J = k = 0, 1, and 2, without invoking an adiabatic separation of high- and low-frequency degrees of freedom. The vibrational ground state resides in the Xe-HI potential well, while the first excited state, 8.59 cm(-1) above the ground, occupies the Xe-IH well. We find that intra-complex dynamics exhibits a sudden transformation upon increase of the r(HI) bond length, accompanied by abrupt changes in the geometric and dipole parameters. A similar chaotic behavior is predicted to occur for Xe:DI at a shorter r(DI) bond length, which implies stronger coupling between low- and high-frequency motions in the heavier complex. Our calculations confirm a strong enhancement for the r(HI) stretch fundamental and a significant weakening for the first overtone vibrational transitions in Xe:HI, as compared to those in the free HI molecule. A qualitative explanation of this, earlier experimentally detected effect is suggested.

Spectroscopic parameters and molecular constants of HI(X1Σ+), DI(X1Σ+) and TI(X1Σ+) isotope molecules

The potential energy curve (PEC) of HI(X1Σ+) molecule is studied using the complete active space self-consistent field method followed by the highly accurate valence internally contracted multireference configuration interaction approach at the correlation-consistent basis sets, aug-cc-pV6Z for H and aug-cc-pV5Z-pp for I atom. Using the PEC of HI(X1Σ+), the spectroscopic parameters of three isotopes, HI(X1Σ+), DI(X1Σ+) and TI(X1Σ+), are determined in the present work. For the HI(X1Σ+), the values of D0, De, Re, ωe, ωeχe, αe and Be are 3.1551 eV, 3.2958 eV, 0.16183 nm, 2290.60 cm−1, 40.0703 cm−1, 0.1699 cm−1 and 6.4373 cm−1, respectively; for the DI (X1Σ+), the values of D0, De, Re, ωe, ωeχe, αe and Be are 3.1965 eV, 3.2967 eV, 0.16183 nm, 1626.8 cm−1, 20.8581 cm−1, 0.0611 cm−1 and 3.2468 cm−1, respectively; for the TI (X1Σ+), the values of D0, De, Re, ωe, ωeχe, αe and Be are of 3.2144 eV, 3.2967 eV, 0.16183 nm, 1334.43 cm−1, 14.0765 cm−1, 0.0338 cm−1 and 2.1850 cm−1, respectively. These results accord well with the available experimental results. With the PEC of HI(X1Σ+) molecule obtained at present, a total of 19 vibrational states are predicted for the HI, 26 for the DI, and 32 for the TI, when the rotational quantum number J is equal to zero (J = 0). For each vibrational state, vibrational level G(v), inertial rotation constant Bv and centrifugal distortion constant Dv are determined when J = 0 for the first time, which are in excellent agreement with the experimental results.

Nitrogen-induced broadening and shifts of rotation-vibrational lines in the fundamental, first, second and third overtone bands of HI

We report experimental results on the previously unknown broadening and shifting coefficients in the fundamental and three overtone vibration–rotation bands of the HI molecule in mixtures with nitrogen gas. Our data are compared with the previously published results for the fundamental bands of the HF and HCl molecules. It is shown that the line shifts are dominated by the vibrational dependence of the isotropic part of the intermolecular interaction potential.

A new crossed molecular beam apparatus using time-sliced ion velocity imaging technique

A new crossed molecular beam apparatus has been constructed for investigating polyatomic chemical reactions using the time-sliced ion velocity map imaging technique. A unique design is adopted for one of the two beam sources and allows us to set up the molecular beam source either horizontally or vertically. This can be conveniently used to produce versatile atomic or radical beams from photodissociation and as well as electric discharge. Intensive H-atom beam source with high speed ratio was produced by photodissociation of the HI molecule and was reacted with the CD(4) molecule. Vibrational-state resolved HD product distribution was measured by detecting the CD(3) product. Preliminary results were also reported on the F+SiH(4) reaction using the discharged F atom beam. These results demonstrate that this new instrument is a powerful tool for investigating chemical dynamics of polyatomic reactions.

Studies on the photodissociation dynamics of HI molecule within the A band range

The photodissociation dynamics of HI molecule has been studied within the A band range. Partial and total extinction cross-sections are obtained from numerical calculations. The frequency dependent branching fraction is determined and agrees with the experiment. The curve-crossing probabilities are derived resorting to the anisotropy data of fragmentation product and the one-dimensional Landau–Zener model is used to examine the possibility that nonadiabatic mechanism occurs in the dissociation process. The results suggest that the contribution of nonadiabatic mechanism to HI photofragmentation, which may be caused by spin–rotational coupling, is not significant over the low energy part of the A band and thus can be ignored, although the angular distribution is less anisotropic in this energy regime.

Theoretical study of the potential energy surface and differential scattering cross sections of He-HI complex

The intermolecular potential energy surface for He-HI complex has been first calculated by employing supermolecule method and the single and double excitation coupled-cluster with a noniterative perturbation treatment of triple excitation CCSD(T) approach using a large basis set containing the bond function set 3s3p2d1f. The potential energy surface has two potential wells. The global minimum with a well depth of 4.473 meV has been found for the linear He-I-H configuration with R，the distance of the He atom and the center of mass of the HI molecule, of 0.363nm. In addition to the global minimum, there is a second minimum corresponding to the linear He-H-I configuration with a well depth of 2.996 meV and R of 0.442nm. Then the analytic expression of the interaction potential for the He-HI complex of the ground state has been obtained by utilizing the Barker potential-type analytic function to fit the calculated intermolecular energy data. On the basis of the above results, the differential scattering cross sections (DCS) at the energy of 100meV for collision between He atom and HI molecule have been calculated using the quantum close-coupling method. Finally, the validity of the potential energy surface of the He-HI system has been verified by comparing it with the CCSD(T) potential energy surface of the He-HX(X=F, Cl, Br) systems and by comparing their DCS at the same collision energy.

Phase control of the photofragment branching ratio of the HI molecule in two intense few-cycle laser pulses

Phase control of the photofragment branching ratio of the HI molecule in two intense few-cycle laser pulses

Spectral line parameters in the (3 ← 0) overtone band of the HI molecule and line-mixing in the band head

The linestrengths, self-pressure broadening and shifting coefficients have been measured for P 3 (10)– R 3 (12) lines in the second overtone band of hydrogen iodide. A dipole moment function in terms of the reduced nuclear displacement x = ( R − R e )/ R e is obtained using rotationless dipole matrix elements determined by the Herman–Wallis analysis of the (1, 2, 3 ← 0) HI bands: μ ( x) = 0.4471(5) − 0.0770(2) x + 0.547(3) x 2 − 1.93(2) x 3, in a full agreement with the function proposed previously [J. Mol. Spectrosc. 223 (2004) 67]. A close match is demonstrated of the results of most recent relativistic calculations [Phys. Chem. Chem. Phys. 6 (2004) 3779] with the spectroscopically derived electric dipole parameters for HI. Line-mixing in the band head is observed, the self-pressure shifting and broadening coefficients for the (3 ← 0) band lines are determined.

Probing atomic and molecular dynamics from within

We have investigated with unprecedented levels of detail photodetachment of negative ions and photoionization of molecules using the brightness, spectral resolution, and tunability of the Advanced Light Source at Lawrence Berkeley National Laboratory. In particular, we report here on investigations carried out in K-shell photodetachment of atomic Li − and He −. We also report on angular distribution of core-level iodine 4d photoelectrons from the HI molecule. In both cases comparison with calculations is discussed.

Study of Dissociative Electron Attachment to HI Molecule by using R-matrix Representation for Green's Function

The new method of calculation of scattering Green's function recently proposed by the authors (G M Mil'nikov, H Nakamura and J Horáček 2001 Comput. Phys. Commun. 135 278) is applied to the process of dissociative attachment of low-energy electrons to HI molecule previously considered by Horáček, Domcke and Nakamura (1997 Z. Phys. D 42 181). The calculation is extended to vibrationally and rotationally excited target gas molecules. The temperature dependence of the dissociative attachment cross section is determined.

On the ultraviolet photofragmentation of hydrogen iodide

An ab initio configuration interaction (CI) study including spin-orbit coupling is carried out for the ground and low-lying excited states of the HI molecule by employing a relativistic effective core potential for the iodine atom. The computed spectroscopic constants for the X 1Σ+ ground and b 3ΠΩ Rydberg states are in good agreement with available experimental data, as are the vertical excitation energies for the repulsive a 3Π1, a 3Π0+, and A 1Π1 states of the A band. The a 3Π0+ state is found to possess a shallow minimum of 600 cm−1 depth outside the Franck–Condon region, at ≈5.1 a0. The electric-dipole moments have also been calculated for transitions from the ground to the A band states. Contrary to what is usually assumed, the a 3Π1, A 1Π1←X0+ transition moments are found to depend strongly on internuclear distance. Employing the computed potential energy and transition moment data, partial and total absorption spectra for the A band are calculated and the I* quantum yields, ΦI*(ν), are determined as a function of excitation energy. The maximal ΦI*(ν) values are calculated to be 0.55–0.59 and lie at 39 000–40 000 cm−1, which agrees well with experimental results. The influence of the t 3Σ1+ state and of the nonadiabatic effects on the ΦI*(ν) values is found to be negligible in the essential part of the A band. Finally, it is shown that significantly higher I* quantum yield values (up to 0.8–0.9) may be achieved when vibrationally hot HI molecules are excited in the appropriate spectral range.

The microwave spectrum and ground-state structure of H2O⋯HI

The microwave spectrum and ground-state structure of H2O⋯HI are reported. The fitted ground-state constants include: A0=428.9 GHz, B0=2189.7351(5) MHz, C0=2175.9546(5) MHz, χaa=−1479.399(10) MHz, (χbb−χcc)=−17.37(1) MHz. Evidence will be presented for a complex that has an R(O–I) distance equal to 3.745(2) Å. The reduction of χaa from the value χ0 in the free HI molecule, corresponds to a zero-point oscillation angle θav=cos−1(〈cos2θ〉1/2)=20.89(2)°. Ab initio calculations support the conclusion that the ground vibrational state for the H2O flapping mode is delocalized between two equilibrium structures at an energy above an inversion barrier.

Reconstitution of Escherichia coli RNase HI from the N-fragment with High Helicity and the C-fragment with a Disordered Structure

The Escherichia coli RNase HI variant with the Lys86-->Ala mutation is purified in two forms, as nicked and intact proteins. The nicked K86A protein, in which the N-fragment (Met1-Lys87) and the C-fragment (Arg88-Val155) remain associated, is enzymatically active. These N- and C-fragments were isolated and examined for reassociation. These peptides did not associate to form the nicked K86A protein at pH 3.0 in the absence of salt, but were associated, with a yield of 30-80%, when the pH was raised to 5.5 or when salt was added. Measurements of the CD spectra show that the alpha-helices are partially formed in the N-fragment at pH 3.0 in the absence of salt and are almost fully formed either at pH 5.5 or at pH 3.0 in the presence of 0.15 M NaCl. In contrast, the C-fragment remains almost fully disordered under these conditions. The N-fragment with this high (native-like) helicity shows the characteristics of a molten globule with respect to the content of the secondary and tertiary structures, the ability to bind a fluorescent probe (1-anilinonaphthalene-8-sulfonic acid), and the behavior on the thermal transition. These results suggest that the N-fragment contains an initial folding site, probably the alpha I-helix, and the completion of the folding in this site provides a surface that facilitates the folding of the C-fragment. This folding process may represent that of the intact RNase HI molecule.

Angle- and spin-resolved photoelectron spectroscopy in rotationally resolved photoionization of HI

The method of angle- and spin-resolved photoelectron spectroscopy has been used in combination with a laser based source of vacuum ultraviolet (VUV) radiation to study the photoionization dynamics of the HI molecule. The narrow bandwidth (Δv<1 cm−1) of the ionizing VUV radiation (v=83 200 cm−1−89 300 cm−1) enables the resolution of the molecular rotation for single-photon excitation to spin-orbit autoionization resonances. The experimental results for the dynamical parameters σ,A, β, ζ, and α are compared to the results of a recent ab-initio calculation (M. Büchner, G. Raseev, and N.A. Cherepkov, J. Chem. Phys.96, 2696 (1992)) and used to analyze the photoionization process in terms of partial contributions of different values ofl and λ to the outgoing electron waves.

Cross section and spin polarization for photoionization of the HI molecule: Rotationally resolved theoretical results in the spin–orbit autoionization region

The theoretical calculations of rotationally resolved total and differential cross sections and spin polarization parameters for the photoionization of HI molecule are presented. These calculations are based on the theoretical expressions derived by Raşeev and Cherepkov [Phys. Rev. A 42, 3948 (1990)]. The transition moments used in the calculation are taken from an ab initio calculation without rotation. Molecular rotation is included in the framework of a simplified model taking into account Hund’s case (c)–(e) frame transformation. The results of ab initio calculations of cross section and electron spin polarization parameters for state-to-state transition are obtained for the first time. Averaged over the rotational levels of the initial state and summed over the rotational levels of the final state of the ion, these calculations are compared with the recent measurements of the total cross section and integrated spin polarization parameters performed in Bielefeld.

Quadrupole hyperfine structure of v=3←0, 6←0 overtone band spectral lines of HI observed with near infrared diode lasers

Diode lasers in the near infrared region are used to observe overtone band transitions (v=3←0, and 6←0) of the HI molecule. From spectral line shape analysis of low J transitions, quadrupole coupling constants eqQ in the v=3, and 6 vibrational states are determined to be −1948±5 and −2066±5 MHz, respectively.

Estimates of relativistic contributions to molecular properties

A simple method for the estimation of the relativistic contribution to atomic and molecular properties is proposed. The method assumes that the dominant portion of relativistic contribution to different properties is accounted for by the Cowan–Griffin operator. In contrast to recently investigated variational relativistic and quasirelativistic approaches, the present method is based virtually on the triple-perturbation theory approach and can be easily executed in the framework of the finite-field perturbation schemes. The method proposed in this paper is applied to the evaluation of the relativistic contribution to electric properties of hydrogen halides. This contribution turns out to be completely negligible in the case of HCl. For the HI molecule, the relativistic correction to its dipole moment becomes almost as important as the electron correlation effects. A similar result is also obtained in the case of the dipole moment of AgH. Different possible applications of the present method are discussed. The major advantage of the proposed perturbation approach is a very simple computational structure which permits the calculation of relativistic corrections from any available nonrelativistic wave function.

Spin polarization of molecular photoelectrons in the case of rotationally resolved photoionization spectra.

A theoretical derivation of the differential photoionization cross section taking into account the spin polarization of photoelectrons is presented. This cross section corresponds to rotationally resolved transitions from an initial rotational level of the neutral molecule to a final rotational level of the ion. The final-state wave function of the ion-plus-electron system is written in the Hund's-case (c) coupling scheme, and the parities of this state and of the initial-state wave functions are explicitly introduced. Two equivalent expressions for the cross section are obtained that correspond to two coupling schemes of the angular momenta involved in the problem. One is a transferred-momentum-coupling scheme, and the other is the final-state (ion-plus-electron) total-angular-momentum-coupling scheme. Their respective advantages in analyzing the experimental results are highlighted. Each term in the transition moment and cross-section expressions contains a multiplicative factor of a simple form that determines if a contribution to these expressions is zero or not, thus playing the role of a selection-rule factor. Our expressions apply to the single-photon process as well as to multiphoton processes in cases in which only the last (one-photon) ionization step is considered explicitly. The paper ends with derivation of explicit formulas for the total cross section and the angle-integrated spin-polarization parameter in a particular case. The photoionization of the HI molecule was the model for these particular formulas.

Theoretical study of the negative ions of HBr and HI.

Relativistic-configuration-interaction (RCI) and complete-active-space (CAS) multiconfiguration self-consistent-field (MCSCF)/CI calculations are performed for the low-lying anion states of ${\mathrm{HBr}}^{\mathrm{\ensuremath{-}}}$ and ${\mathrm{HI}}^{\mathrm{\ensuremath{-}}}$. At both the RCI and CASSCF/CI levels of theory, the $^{2}\mathrm{\ensuremath{\Sigma}}^{+}$ anion states are found to be repulsive in the Franck-Condon regions of the HX $^{1}\ensuremath{\Sigma}^{+}$ states and bound relative to the H+${X}^{\mathrm{\ensuremath{-}}}$ asymptotes at r&gt;${r}_{e}$ of the parent neutral states. The HI molecule is predicted to have a slightly positive adiabatic electron affinity, and electron attachment in this system is considered in a Langevin model. Electronic transition moments between the $^{2}\mathrm{\ensuremath{\Sigma}}_{1/2}^{+}$ and $^{2}\mathrm{\ensuremath{\Pi}}_{1/2}$ states of ${\mathrm{HBr}}^{\mathrm{\ensuremath{-}}}$ and ${\mathrm{HI}}^{\mathrm{\ensuremath{-}}}$ are calculated in order to examine the origins of nonadiabatic ${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$ fragment production observed in dissociative-attachment experiments on HBr.