Br 3d Research Articles

Atomic Auger decay in core-excitedHBrby angle-resolved two-dimensional photoelectron spectroscopy

Angle-resolved two-dimensional photoelectron spectroscopy has been used to study HBr in the vicinity of the Br 3d ionization thresholds. The energy positions of the two 3d{sub 5/2,3/2}{yields}{sigma}{sup *} resonances have been measured directly and found to be at 70.89(6) eV and 71.92(6) eV, respectively, giving a spin-orbit splitting of 1.03(3) eV for the two Br 3d components. Br Auger lines (26 eV<KE<54 eV), produced by dissociation of HBr after 3d{yields}{sigma}{sup *} transitions, are tentatively assigned according to their kinetic-energy positions and their profiles as a function of photon energy are found to be asymmetric. The angular distribution asymmetry parameters {beta} of these lines, which have not been measured before, have also been derived. The alignment parameters for the two intermediate atomic states ({sup 2}D{sub 5/2} and {sup 2}D{sub 3/2}) have been found and used to derive intrinsic anisotropy parameters {alpha}{sub 2} from the {beta} parameters. These were found to be similar to those of the equivalent M{sub 4,5}NN normal Auger lines in the isoelectronic counterpart Kr calculated by Tulkki et al. [Phys. Rev. A 48, 1277 (1993)].

XPS characterization of the surface immobilization of antibacterial furanones

Brominated furanones have attracted recent interest as antibacterial compounds. To utilize them as protective coatings in biomedical device applications, they must be covalently immobilized onto solid surfaces; however, interfacial coupling protocols developed for other biomolecules are not applicable to furanones. An azide reaction scheme has enabled covalent immobilization onto fluorinated ethylene propylene copolymer but its chemistry is less predictable, requiring detailed characterization by XPS and tapping mode AFM after each step of the immobilization sequence. XPS curve fitting resolved components in the C 1s, N 1s and Br 3d regions. Angle dependent XPS was used to assess the depth distributions and layer thicknesses. The results indicated successful covalent immobilization of furanones; however, side reactions occurred. In addition to the expected C Br, a contribution from bromine ion (Br −) was detected, indicating that photo-degradation of furanones took place during UV illumination, and this reaction was found to increase with illumination time. The Br − was removed by washing with water, whereas the C Br signal from immobilized furanone remained. Spectroscopic characterization will assist in elucidating the structure of furanone coatings, understanding their mode of action when covalently immobilized on surfaces, and rationally designing and optimizing an effective antibacterial coating for biomedical applications.

Influence of formation path on the CH2BrCl2+ dissociation dynamics

To get further insight into the CH2BrCl site-selective fragmentation previously observed upon inner-shell ionization, we have performed high-resolution Br 3d and Cl 2p Auger and spin-orbit resolved Br 3d Auger spectra, and studied the dissociation properties of the CH2BrCl2+ dication formed at threshold by means of threshold electron pair-ion coincidence measurements. The key point is that the origin of site-specific bond breaking is found in the Auger decay itself, as it preferentially populates selected dication states. Whereas the predominance of the C-Br bond breaking is observed in both threshold and inner-shell studies, no signature of selective C-Cl rupture is reported for the dication formed at threshold.

Absolute photoabsorption cross-sections (oscillator strengths) for valence and inner shell excitations in hydrogen chloride, hydrogen bromide and hydrogen iodide

Absolute photoabsorption cross-sections (oscillator strengths) have been measured for the valence shell and selected (Cl 2p, Br 3d and I 4d) inner shell excitations in HCl, HBr and HI, respectively at photon energies up to 280 eV using dipole (e,e) spectroscopy. Absolute scales are established using the S(0) and S(−2) sum rules.

Negative photoion spectroscopy of the core-excited bromo-chloro-alkanes, Br(CH2)nCl, n = 1–4

Polar photodissociation of a set of bromo-chloro-alkanes in the vicinity of the Br 3d core edge has been observed for the first time. It is shown that negative photoion spectroscopy is a powerful tool for investigating the various decay mechanisms of core-excited molecules. Analysis of these results indicates that the observed polar photodissociation arises from two competing spectator Auger decay processes in which the molecule can dissociate either before or after the core hole relaxation.

A study of the photoionisation dynamics of the cyanogen halides

The valence shell photoelectron spectra of BrCN and ICN have been studied using synchrotron radiation. In addition to the main bands associated with the single-hole states, complex satellite structure due to many-electron effects has been observed in the inner valence region. The Green’s function method has been employed to evaluate the ionisation energies and pole strengths of all valence states and the results have facilitated an interpretation of the experimental spectra. Photoelectron angular distributions and branching ratios for the valence shell, the Br 3d level in BrCN and the I 4d level in ICN have been measured in the photon energy range 14–120 eV. The continuum multiple scattering (CMS-Xα) approach has been used to calculate photoelectron asymmetry parameters and branching ratios for the valence orbitals of ClCN, BrCN and ICN. These have been used to assess the influence of Cooper minima and shape resonances on the photoionisation dynamics. In ICN, the experimental and theoretical results provide evidence of core-valence shell coupling at energies above the I 4d threshold. The experimentally determined asymmetry parameters and branching ratios for the spin–orbit split Br 3d5/2,3/2 and I 4d5/2,3/2 components have been compared to those for Kr and Xe, and a strong atomic-like behaviour is evident. The calculated spin–orbit averaged β-parameters for the Br 3d and I 4d levels confirm this interpretation. Hartree–Fock (HF) calculations have been carried out to study the evolution of the valence orbital characteristics through the series of halogen-substituted XCN (X=H, Cl, Br, I) molecules.

Dissociative adsorption and thermal desorption of dibromoethylene on Si(1 0 0)2 × 1: surface mediated dehalogenation and recombinative evolution of HBr

The room-temperature (RT) adsorption of dibromoethylene on Si(1 0 0)2 × 1 has been investigated by X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD) mass spectrometry. The C 1s and Br 3d XPS spectra indicate the presence of a mono-σ bonded vinyl bromide adspecies (30%) and a di-σ bonded vinylene adspecies (70%) on Si(1 0 0)2 × 1, which suggests dehalogenation of dibromoethylene producing one or both Br atoms upon RT adsorption. Annealing the sample to 645 K for 30 min completely removes the vinyl bromide adspecies, leaving behind the di-σ bonded vinylene. Recombinative desorption of HBr from the 2 × 1 surface has been observed over the temperature range 800–1000 K upon further annealing. The adsorption and desorption behaviour of dibromoethylene on Si(1 0 0)2 × 1 is found to be consistent with an insertion reaction mechanism, in marked contrast to the cycloaddition reaction mechanism observed for ethylene or acetylene on Si(1 0 0)2 × 1. The present work illustrates the surprisingly rich chemical activity of the 2 × 1 surface in facilitating dehalogenation of prototypical halogenated alkenes.

Electronegativities from core-ionization energies: electronegativities of SF5 and CF3.

Core-ionization energies have been measured for SF(6) (S 2p), SF(5)SF(5) (S 2p), SF(5)Br (S 2p and Br 3d), and SF(5)CF(3) (S 2p and C 1s). These results, together with others that establish correlations between core-ionization energies and Pauling electronegativities, make it possible to assign group electronegativities to SF(5) and CF(3). This method gives electronegativities for these groups comparable to that of bromine, whereas analysis of the effect of these groups on acidity indicates electronegativities comparable to that of fluorine. Other methods of estimating electronegativity fall between these extremes. These disparities can be understood in part as reflecting the effects of polarizibility of the substituent, which tends to lower both the core-ionization energy and the deprotonation energy, making the electronegativity appear to be less in one case and more in the other. In addition, and possibly more important, the core-ionization energies presented here reflect the effect of the group on an adjacent atom, whereas the acidity reflects the effect on a remote atom. It appears that fluorine has a large effect on an adjacent atom but a relatively small effect on a remote atom. By contrast SF(5) and CF(3) have a relatively small effect on an adjacent atom, but this effect falls off only slowly with distance from the substituent. Thus, the effective electronegativities of CF(3) and SF(5) relative to those of the halogens depend on the site at which the molecule is probed as well as on the process that is under consideration.

Ionic pathway studies in fragmentation of the core-excited (CH 3) 3SiBr molecule involving the Br(3d) and Si(2p) inner-shells in the range of 60–133 eV

Dissociative multiple photoionization of bromotrimethylsilane [(CH 3) 3SiBr] has been probed in the valence, the Br(3d), and the Si(2p) core-level photoexcitation/photoionization regions by time-of-flight (TOF) mass spectrometry and photoion–photoion coincidence (PIPICO) method together with linearly polarized synchrotron radiation. The inner-shell photoionization spectra are dominated by a huge resonance attributed to the diffusion of the outgoing photoelectrons by the centrifugal barrier for the Br(3d 9 ϵf ) outgoing channel. In addition to the giant resonance, discrete photoabsorption bands below the Br(3d 5/2) and Si(2p 3/2) thresholds have been observed in both the total photoion and PIPICO yield spectra. In the valence excitation/ionization region, single ionization leading to the formation of C n H p SiBr +( n=0–3), C n H p Si +( n=0–3), and CH 3 + prevails. Above the Br(3d) threshold including the Si(2p) region, however, destruction of the three or more bonds could account for the dominant PIPICO channels leading to the formation of H +–CH p +( p=1–3) and CH n +–H p Si +( p=0,1) ion pairs. The exclusive formation of only the singly charged ions over the entire energy range indicates that charge redistribution is much faster than the bond cleavages.

Auger decay widths of the ligand-field-split Br 3d components in the HBrmolecule

In this paper, high resolution Br 3d photoelectron spectra of HBr are presented.Experimental lifetime widths of the ligand-field-split Br 3d components have beenderived, and compared with theoretical predictions based on the one-centreapproximation accounting for relativistic effects. The dependence of thetheoretical decay widths on the kinetic energy for the Auger electron and thecorrelation in the final states of the Auger decay has also been investigated.

Dissociative multiple photoionization of SiBr 4 and GeBr 4 in the VUV and X-ray regions: a comparative study of inner-shell processes involving Si(2p, 2s), Ge(3d, 3p, 3s), and Br(3d, 3p, 3s)

Dissociative multiple photoionization of MBr 4 (M=Si, Ge) in the Si(2p, 2s), Ge(3d, 3s, 3p), and Br(3d, 3p, 3s) inner-shell regions has been studied by using time-of-flight (TOF) mass spectrometry coupled to synchrotron radiation in the ranges of 50∼944 eV for SiBr 4 and 50∼467 eV for GeBr 4. Total photoion and photoion–photoion coincidence (PIPICO) yields have been measured as functions of the photon energy. Here, giant shape resonances have been observed beyond the thresholds of the 3d shells owing to the Br(3d 10)→Br(3d 9 ϵf) excitation, showing the similar patterns for both of the systems. The ranges and the intensities of the shape resonances are found to be tremendously broad and enhanced, respectively, by the tetrahedral arrangement of the bromine ligands. In addition to the giant resonances, we have observed discrete features corresponding to the Br(3d), Si(2p), and Si(2s) in SiBr 4and to the Br(3d), Ge(3p), and Ge(3s) in GeBr 4. The dissociation processes of multiply charged parent ions have also been evaluated from the variations of photoelectron–photoion coincidence (PEPICO) and PIPICO yields with the photon energy. Over the entire energies examined, most efficient PIPICO channels involve Br +–Br +, Br +–MBr +, and M +–Br + (M=Si, Ge), the formation of which indicates that the total destruction of the molecules is a dominant process in the dissociative photoionization of the molecules.

Dissociative multiple photoionization of Br 2, IBr, and I 2 in the VUV and X-ray regions: a comparative study of the inner-shell processes involving Br(3d,3p,3s) and I(4d,4p,4s,3d,3p)

Dissociative multiple photoionization of the bromine, the iodine monobromide, and the iodine molecules in the Br(3d,3p,3s) and I(4d,4p,4s,3d,3p) inner-shell regions has been studied by using time-of-flight (TOF) mass spectrometry coupled to synchrotron radiation in the ranges of 90∼978 eV for Br 2, 60∼133 eV for IBr, and 86∼998 eV for I 2. Total photoion and photoion–photoion coincidence (PIPICO) yields have been recorded as functions of the photon energy. Here, giant shape resonances have been observed beyond the thresholds of the inner-shells owing to the Br(3d 10)→Br(3d 9 ϵf), I(4d 10)→I(4d 9 ϵf), and I(3d 10)→I(3d 9 ϵf) transitions. The dissociation processes of the multiply charged parent ions have also been evaluated from variations of photoelectron–photoion coincidence (PEPICO) and PIPICO spectra with the photon energy. From each Br(3p 3/2) (189.9 eV) and I(4p 3/2) threshold (129.9 eV), quintuple ionization of the molecules begins to play important roles in the photoionization, subsequently yielding ion pairs of X 3+–X 2+ (X=Br, I). From the I(3d 5/2) threshold (627.3 eV), loss of six electrons from iodine molecule additionally begins to play a minor role in the multiple photoionization, giving rise to the formation of ion pairs of either I 3+–I 3+ or I 4+–I 2+. A direct comparison of the strengths and the ranges of the I(4d) and Br(3d) giant resonances was successfully made from dissociative photoionization of IBr. Over the entire energy range examined, 60< E<133 eV, biased charge spread relevant to the specific core-hole states of IBr is observed, presumably reflecting the fact that charge localizes mostly in the excited atoms, which can be accounted for mainly by a two step decay via a fast dissociation followed by autoionization upon the VUV absorption.

Dissociation processes of core-excited CBr 4 involving the Br(3d, 3p, 3s) and C(1s) inner-shells in the range 50–460 eV

The dissociative multiple photoionization of CBr 4 in the valence, and in the Br(3d, 3p, 3s) and C(1s) inner shell regions has been studied by using time-of-flight (TOF) mass spectrometry coupled to synchrotron radiation in the range 50–460 eV. Total and individual photoion yield curves have been recorded as a function of the photon energy. Several discrete resonances are observed below the Br(3d) threshold region. Also a giant shape resonance in the total ion yield curve is observed beyond the Br(3d) region, which can be identified as a shape resonance owing to the diffusion of the outgoing photoelectron by the angular momentum barrier in the 3d 9ϵf outgoing channel. Various monocations of Br + and CBr n + ( n=0–3) are detected along with dications of Br 2+ and CBr 3 2+ in the whole energy range examined. Dissociation processes of multiply charged CBr 4 parent ions have also been investigated by photoelectron–photoion coincidence (PEPICO) and photoion–photoion coincidence (PIPICO) methods. The dominant dissociation pattern is found to involve C +–Br + and Br +–Br + in the whole energy range examined. Distinct energy dependence of dissociation processes is observed in the Br(3p) and Br(3s) regions. With the help of ab initio HF/6-311++G(d) calculation, we estimated the photoabsorption positions and symmetries for the discrete core-excited states using the Z+1 equivalent ionic core model. The specific excitation and dissociation of molecules provides information on energy dissipation processes in conjunction with the relevant core hole states.

Variable-energy photoelectron spectroscopy of substituted rhenium and manganese pentacarbonyls: molecular orbital assignments and the interatomic resonant effect.

High-resolution variable-energy photoelectron spectra of M(CO)5X [M = Re, X = Re(CO)5, Cl, Br, and I; and M = Mn, X = Mn(CO)5 and Br] are reported. Tunable synchrotron radiation is used to distinguish the Re 5d and Br 4p orbital based peaks for the controversial Re(CO)5Br. Our results provide firm molecular orbital assignments for all of these molecules. The valence orbital in the ordering of ionization energies for M(CO)5Cl (M = Mn and Re) and Mn(CO)5Br is a 1(M-X) > e(X) > b2(M) > e(M); but for M(CO)5I (M = Mn and Re) and Re(CO)5Br the ordering is a1(M-X) > e(M) > b2(M) > e(X). The crossover of the HOMO in the Re molecules due to the change in the halogen electronegativities occurs at Re(CO)5Br. The metal np-->nd resonance is observed for all of these molecules. For molecules like M2(CO)10 (M = Re and Mn) and Mn(CO)5Br, the observation of this np-->nd resonance is useful in assigning the metal nd based orbitals in their valence level spectra. However, for molecules like Re(CO)5X (X = Br and Cl), a np-->nd type resonance is observed on bands arising from both Re 5d and halogen mp based orbitals. This new resonant effect on the ligand-based orbitals is shown to be mainly due to the interatomic resonant effect. The core and valence level chemical shifts of these compounds are treated using Jolly's approach to confirm the assignments for the valence level spectra of some of these molecules. The high-resolution inner valence and core level spectra of these compounds are reported. Broadening of Re 4f, Br 3d, and I 4d core level spectra is discussed. The Auger peaks are observed in the high-resolution, high-intensity Br 3d of Re(CO)5Br and I 4d of Re(CO)5I spectra.

Cross sections and values for ligand-field-split Br 3d orbitals in HBr

The ligand field in HBr results in the splitting of the Br 3d orbitals into the 3d (dx2-y2, dxy), 3d (dxz, dyz), and 3d (dz2) orbitals. In core ionized HBr, the stronger spin-orbit splitting removes the remaining degeneracies and results in five different Br 3d eigenstates from linear combinations of the 3d, 3d, and 3d orbitals. In high-resolution Br 3d photoelectron spectra, as presented in this work, these five peaks are resolved. The photoelectron cross sections and values for the different d orbitals have been studied from 5 to 25 eV above threshold. The relative intensities for the different 3d orbitals are quite different at different analysis angles, showing that the values are different. Multiple-scattering-X calculations give results in semiquantitative agreement with experiment.

Dissociative Multiple Ionization following Valence, Br(3d), and Si(2p) Inner Shell Photoexcitation of SiBr4 in the Range of 30−133 eV

The photoionization of SiBr4 in the valence shell, and the Br(3d) and Si(2p) inner shell excitation/ionization regions, has been studied by using a time-of-flight mass spectrometer and synchrotron radiation over the range 30−133 eV. The photoionization efficiency curve of SiBr4 has been recorded as a function of the incident photon energy. Dissociation processes of SiBr4 have also been investigated by photoelectron−photoion coincidence and photoion-photoion coincidence (PIPICO) techniques. Various monocations of Brn+ (n = 1, 2) and SiBrn+ (n = 0−4) are detected along with dications of Br2+ and SiBrn2+ (n = 0, 1, 3) in the energy range. Various dissociation patterns are proposed based on the measurements of the ion time-of-flight differences in the PIPICO mode. The dominant dissociation pattern is found to be Si+−Br+ and SiBr+−Br+ in the whole energy examined. In the Br(3d) excitation region, however, a fragmentation leading to ion pair such as SiBr3+−Br+ also plays an important role in the dissociation of...

High-resolution photoabsorption and photoelectron spectra of bromine-containing molecules at the Br 3d edge: the importance of ligand field splitting

Using monochromatic synchrotron radiation, we have recorded high-resolution Br 3d photoelectron and photoabsorption spectra (PES and PAS, respectively) for the five molecules: HBr, DBr, and . The Br 3d PES of HBr, DBr and show five peaks due to the combined effects of ligand field (or molecular field) and spin - orbit splitting. The and PES are vibrationally broadened, but also show additional broadening from ligand field splitting. The Br 3d ligand field splittings (as quantified by the crystal field parameter) are similar to the I 4d values for the iodine analogues, and increase in the order of . The Br 3d binding energies also increase in the above order due to the increasing electronegativity of the substituents. The very complex Br 3d photoabsorption spectra also show the same ligand field/spin - orbit splitting which split each transition into five transitions. These spectra are dominated by the peaks from the five transitions; but a myriad of other peaks from the (n = 4, 5), np (n = 6 - 9), ns (n = 6, 7) and nf (n = 4, 5) transitions are required to fit these spectra. Good fits to all the spectra have been obtained using ligand field splittings which are similar to the PES results, and quantum defects for s, p, d and f orbitals of , 1.6 - 2.0 and 0.8 - 1, respectively.

Absolute photoabsorption and photoionization studies of methyl bromide using dipole electron impact and synchrotron radiation PES techniques

Absolute oscillator strengths (cross sections) have been measured for the photoabsorption of CH 3Br at low resolution (1 eV fwhm) in the equivalent photon energy range from 6 to 450 eV and at high resolution (0.05 eV fwhm) from 5 to 100 eV using dipole (e,e) spectroscopy. In the valence shell and Br 3d inner shell regions of CH 3Br, from the first ionization threshold to 79 eV, the photoionization efficiency, ionic photofragmentation branching ratios and absolute partial oscillator strengths for molecular and dissociative photoionization have been determined by dipole (e,e+ion) spectroscopy. The major ionic pathways of the dipole induced breakdown scheme of CH 3Br have been predicted from these results and the partial photoionization oscillator strengths for production of the valence shell electronic states of CH 3Br + have been estimated. Photoelectron branching ratios for CH 3Br have been measured using monochromated synchrotron radiation at photon energies from 21 to 68 eV. These have been combined with the dipole (e,e) photoabsorption data to obtain partial photoionization oscillator strengths for production of the electronic states of CH 3Br +, which have been compared with the partial oscillator strength estimates derived from the (e,e+ion) data.

Ionic photofragmentation (11.5–160 eV) and PIPICO spectroscopy (40–130 eV) of BrCN in the valence shell and bromine 3d regions

Molecular and dissociative photoionization branching ratios and photofragment appearance potentials of BrCN have been determined using dipole (e, e + ion) spectroscopy at equivalent photon energies from the first ionization threshold up to 160 eV. Absolute partial photoionization oscillator strengths (cross sections) for the molecular and dissociative photoions have been obtained from the triple product of the photofragment branching ratio, the photoionization efficiency, and the previously reported absolute photoabsorption oscillator strength [Olney et al., Chem. Phys. 201 (1995) 505]. Information on the Coulomb explosion decay channels of doubly and triply charged molecular ions has been obtained from photoion-photoion coincidence (PIPICO) spectroscopy using synchrotron radiation as a light source in the 40–130 eV photon energy range. While stable doubly charged ions are formed in both the valence and the Br 3d regions no stable triply charged ions are observed. However, the PIPICO measurements detect time correlated singly and doubly charged fragment species resulting from Coulomb explosion of triply charged ions which are first formed at the Br 3d excitation threshold and throughout the ionization continuum by triple autoionization and double Auger type processes. The experimental results provide information on the dipole induced breakdown pathways resulting from valence shell and Br 3d ionization processes in BrCN.

Absolute photoabsorption of BrCN in the valence shell and the bromine M, carbon K and nitrogen K shell regions (5–450 eV)

Absolute oscillator strengths (cross sections) for photoabsorption by BrCN have been measured throughout the VUV and soft X-ray regions (5–451 eV) using dipole (e,e) spectroscopy at both high (0.05–0.10 eV fwhm) and low (1 eV fwhm) resolution. Measurement of the valence shell oscillator strengths are compared with the very limited direct optical data in the literature. For the sharper (Rydberg) bands and the presently determined dipole (e,e) oscillator strengths are considerably larger indicating that significant line saturation (bandwidth) errors are occurring in the previously published direct optical (Beer-Lambert law) measurements. The first absolute measurements and inner shell photoabsorption spectra are reported in the carbon K (1s), nitrogen K (1s) and bromine M (3d, 3p and 3s) regions of BrCN. The carbon and nitrogen 1s spectra show vibrational resolution in the respective, strongly resonance enhanced, 3π(π∗) ← 1s bands. The Br 3d spectrum of BrCN shows clear evidence of ligand field splittings in the 3d52(δ, π and gS) and 3d32(δ and π) excitations to the 5p Rydberg states. The first estimates of the inner shell ionization potentials for the C 1s and N 1s core orbitals of BrCN are obtained from density functional theory calculations. The Br 3d52,32, ligand field inner shell ionization energies are estimated using the 5p←Br 3d excitation energies and considerations of the (transferable) 5p Rydberg term values from the C 1s, N 1s and valence shell spectra.