HeI Photoelectron Research Articles

Simulating the HeI photoelectron spectrum of Cl2O with new full-dimensional adiabatic potential energy surfaces of Cl2O(X̃1A1), Cl2O+(X̃2B1), and Cl2O+(C̃2A2) and a three-state diabatic potential energy matrix of Cl2O+(Ã2B2, B̃2A1, and 22A1): a quantum mechanical study.

To interpret the HeI photoelectron spectrum of Cl2O (involving four lowest electronic states of Cl2O+), in this work we first constructed the associated adiabatic full-dimensional potential energy surfaces (PESs) of Cl2O(X̃1A1), Cl2O+(X̃2B1), and Cl2O+(C̃2A2) and a diabatic potential energy matrix (PEM) of Cl2O+(Ã2B2, B̃2A1, and 22A1) using the explicitly correlated internally contracted multi-reference configurational interaction with Davidson correction (MRCI-F12+Q) and neural network methods. Particularly for the Ã2B2, B̃2A1, and 22A1 states of Cl2O+ coupled in terms of conical intersection, their diabatization is achieved by the neural network approach based merely on the associated adiabatic energies. With the help of newly constructed adiabatic PESs and the diabatic PEM, the HeI photoelectron spectrum of Cl2O is further computed quantum mechanically. The calculated photoelectron spectrum is found to be in good accord with experiment. The mode specificity in the HeI photoelectron bands of Cl2O is analyzed in detail.

THE PHOTOELECTRON SPECTROSCOPY OF THE DICHLOROETHYLENES: THE VICINAL ISOMER trans-1,2-HClC=CHCl. QUANTUM CHEMICAL CALCULATIONS AND EXPERIMENT

The photoelectron spectrum (PES) of trans-1,2-C2H2Cl2 has been measured with the resonance lines in He, Ne and Ar. These spectra are compared to the threshold photoelectron spectrum (TPES) recorded using synchrotron radiation. Nine mostly well separated photoelectron bands are observed at adiabatic ionization energies of 9.633 eV, 11.840 eV, 12.044 eV, 12.582 eV, 13.581 eV, 14.081 eV, 15.724 eV and at about 16.325 eV and 19.00 eV. Most of them exhibit a well resolved and extended vibrational structure. The He-I photoelectron band associated with the ground electronic state of the ion and the corresponding TPES band are characterized by a vibrational structure extending over 0.7 eV and 2.0 eV respectively. In the latter case the strong correlation between the TPES and the photoabsorption spectrum in the same energy region has been established. Several excited states also show an extended vibrational structure. The assignments of the electronic bands and of the vibrational wavenumbers were supported by quantum chemical calculations. The good correlation between predicted vibrational wavenumbers and the experimental values allowed us to assign most of the vibrational structures. The constant ion state (CIS) spectra have been recorded and discussed for selected vibrational levels of the ground state and for the adiabatic transition to the first excited state of the ion.

Photoelectron spectroscopy of (thio)carbonyl compounds

The electronic structures of an unsaturated amide, thioamide and dithionoester have been studied in the gas phase by HeI photoelectron spectroscopy and quantum chemical calculations. The comparison of measured spectra with the spectra of related compounds reveals the effects of intramolecular interactions in these molecules. The electronic structures deduced from the spectra are then related to some of their chemical properties.

Electronic structure of adducts of Eu(III) TRIS-β—diketonates with phenanthroline: photoelectron and theoretical studies

By UPS spectroscopy of vapor, XPS spectroscopy of the condensed phase, and quantum chemical methods the adducts of tris-β-diketonates Eu(асас)3Phen and Eu(hfас)3Phen are studied. The electronic structure and features of the nature of chemical bonds in the adducts are established. The geometric structure of the studied compounds in the gas phase is determined. A procedure is developed that helps to assign the bands in gas-phase HeI photoelectron spectra and also in the valence band of the XPS spectra. Quantum chemical calculations (DFT) make it possible to find the regular changes in the electronic structure of the chelate complexes depending on ligand fluorination, to study the effect of a 1,10-phenanthroline molecule on the electronic structure of the chelate rings, and also to analyze the electronic effects caused by trifluoromethyl substitution for methyl groups in the ligand.

Electronic properties of FC(O)SCH2CH3. a combined helium(I) photoelectron spectroscopy and synchrotron radiation study.

The valence electronic properties of S-ethyl flouromethanethioate (S-ethyl fluoromethsanethioate), FC(O)SCH2CH3, were investigated by means of He(I) photoelectron spectroscopy in conjunction with the analysis of the photofragmentation products determined by PEPICO (phtoelectron-photoion-coincidence) by using synchrotron radiation in the 11.1-21.6 eV photon energy range. The first band observed at 10.28 eV in the HeI photoelectron spectrum can be assigned with confidence to the ionization process from the HOMO [nπ(S) orbital], which is described as a lone pair formally localized on the sulfur atom, in agreement with quantum chemical calculations using the outer valence Green function method [OVGF/6-311++G (d,p)]. One of the most important fragmentation channels also observed in the valence region corresponds to the decarbonylation process yielding the [M-CO](·+) ion, which is clearly observed at m/z = 80. Moreover, S 2p and S 2s absorption edges have been examined by measuring the total ion yield spectra in the 160-240 eV region using variable synchrotron radiation. The dynamic of ionic fragmentation following the Auger electronic decay has been evaluated with the help of the PEPIPICO (photoion-photoion-photoelectron-coincidence spectra) technique.

Symmetry adapted cluster–configuration interaction calculation of the photoelectron spectra of famous biological active steroids

The photoelectron spectra of some famous steroids, important in biology, were calculated in the gas phase. The selected steroids were 5α-androstane-3,11,17-trione, 4-androstane-3,11,17-trione, cortisol, cortisone, corticosterone, dexamethasone, estradiol and cholesterol. The calculations were performed employing symmetry-adapted cluster/configuration interaction (SAC–CI) method using the 6-311++G(2df,pd) basis set. The population ratios of conformers of each steroid were calculated and used for simulating the photoelectron spectrum of steroid. It was found that more than one conformer contribute to the photoelectron spectra of some steroids. To confirm the calculated photoelectron spectra, they compared with their corresponding experimental spectra. There were no experimental gas phase HeI photoelectron spectra for some of the steroids of this work in the literature and their calculated spectra can show a part of intrinsic characteristics of this molecules in the gas phase. The canonical molecular orbitals involved in the ionization of each steroid were calculated at the HF/6-311++g(d,p) level of theory. The spectral bands of each steroid were assigned by natural bonding orbital (NBO) calculations. Knowing the electronic structures of steroids helps us to understand their biological activities and find which sites of steroid become active when a modification is performing under a biological pathway.

Electronic structure of two precursors for nanofabrication: [(CH3)3CN]2W[N(CH3)2]2 and Ti(NMe2)2(NEt2)2.

The electronic structures of bis(tert-butylimino)bis(dimethylamino) tungsten and bis(N-ethylethanaminato)bis(N-methylmethanaminato) titanium heteroleptic complexes, which are precursors for atomic layer deposition of metallic nitride on surfaces, have been investigated by HeI and HeII UV photoelectron spectroscopy and DFT/OVGF calculations. We discuss the electronic structures of these two and other related d(0)-type complexes in relation to the mechanism of adsorption and decomposition of metal alkylamide precursors on surfaces.

The electronic structure of TEMPO, its cation and anion

The electronic structure of TEMPO (2,2,6,6-tetramethyl-1-piperidinyl N-oxide), its cation and anion were studied experimentally using the following electron spectroscopy techniques: electron energy-loss spec-troscopy (EELS), measurement of elastic and vibrational excitation (VE) cross sections, HeI photoelectron (PE) spectroscopy and dissociative electron attachment (DEA) spectroscopy.

Electronic Structure of 1,2‐Dihydro[1,3,2]diazaborolo[1,5‐ a ]pyridine in Comparison with the Parent Isoindole

Gas-phase He-I photoelectron spectra of N-tert-butyl-1,2-dihydro[1,3,2]diazaborolo[1,5-a]pyridine (3) and its thermolysis product, the parent compound 1, have been recorded and assessed by density functional theory calculations. Similarly, N-tert-butylisoindole (4) and the parent isoindole (2) were also studied. The first ionization energies of these compounds increase in the series 3 (6.75 eV)< 1 (6.85 eV)< 4 (6.9 eV)< 2 (7.3 eV). Interestingly, the HOMOs of 1 and 3 are destabilized with respect to the first ionization energy of the isomeric 1,3,2-benzodiazaboroles (ca. 7.3 eV). The dipole moment of the ground state of isoindole derivative 4 (3.48 D) is significantly greater than that of 1,2-dihydro[1,3,2]diazaborolo[1,5-a]pyridine (3; 0.996 D). Upon electronic excitation, the dipole moments increased to 5.945 and 4.735 D for 4 and 3, respectively.

The electronic structure of TEMPO, its cation and anion

The electronic structure of TEMPO (2,2,6,6-Tetramethylpiperidine-N-oxyl) and its cation and anion were studied experimentally using the electron spectroscopy techniques, dissociative electron attachment (DEA) spectroscopy, electron energy-loss spectroscopy, measurement of elastic and vibrational excitation (VE) cross sections and HeI photoelectron spectroscopy. The experiments were supplemented by quantum-chemical calculations of excitation energies, ionisation potential and the Franck–Condon profile of the first photoelectron band. Electron energy-loss spectra were recorded up to 12 eV and revealed a number of bands that were assigned to two valence and a number of Rydberg transitions. VE cross sections reveal a broad band in the 3–12 eV range, assigned to σ* shape resonances and signals in the 0–1 eV range, assigned to a shape resonance corresponding to a temporary capture of the incident electron in the (already singly occupied) π* orbital. Narrow threshold peaks in the VE cross sections are assigned to dipole-bound resonances. The major DEA fragment was found to be O−, with bands at 5.0 and 6.87 eV, assigned to core excited resonances.

Threshold photoelectron spectroscopy of acetaldehyde and acrolein

High-resolution (6meV and 12meV) threshold photoelectron (TPE) spectra of acetaldehyde and acrolein (2-propenal) have been recorded over the valence binding energy region 10–20eV, employing synchrotron radiation and a penetrating-field electron spectrometer. These TPE spectra are presented here for the first time. All of the band structures observed in the TPE spectra replicate those found in their conventional HeI photoelectron (PE) spectra. However, the relative band intensities are found to be dramatically different in the two types of spectra that are attributed to the different dominant operative formation mechanisms. In addition, some band shapes and their vertical ionization potentials are found to differ in the two types of spectra that are associated with the autoionization of Rydberg states in the two molecules.

Theoretical and Experimental Study of Valence Photoelectron Spectrum of d,l-Alanine Amino Acid

In this work, the He-I (21.218 eV) photoelectron spectrum of D,L-alanine in the gas phase is revisited experimentally and theoretically. To support the experiment, the high level ab initio calculations were used to calculate and assign the photoelectron spectra of the four most stable conformers of gaseous alanine, carefully. The symmetry adapted cluster/configuration interaction (SAC-CI) method based on single and double excitation operators (SD-R) and its more accurate version, termed general-R, was used to separately calculate the energies and intensities of the ionization bands of the L- and D-alanine conformers. The intensities of ionization bands were calculated based on the monopole approximation. Also, natural bonding orbital (NBO) calculations were employed for better spectral band assignment. The relative electronic energy, Gibbs free energy, and Boltzmann population ratio of the conformers were calculated at the experimental temperature (403 K) using several theoretical methods. The theoretical photoelectron spectrum of alanine was calculated by summing over the spectra of individual D and L conformers weighted by different population ratios. Finally, the population ratio of the four most stable conformers of alanine was estimated from the experimental photoelectron spectrum using theoretical calculations for the first time.

The spectroscopy of the geminal ethylene difluoride (1,1-C2H2F2): the HeI, threshold and constant ion state photoelectron spectroscopies

The threshold photoelectron spectrum (TPES) and the constant ion state (CIS) spectra of the individual ionic states of 1,1-C2H2F2 have been recorded using synchrotron radiation. The TPES has been measured between 9.5 and 28 eV photon energy. For comparison, the HeI photoelectron spectrum (HeI-PES) has also been measured and analysed in detail. Numerous vibrational structures, reported for the first time, observed in the ground state and the seven excited states of the cation are analysed. Quantum chemical calculations have been performed and provided support to the assignments. The exceptional contribution of autoionization to the HeI-PES could be emphasized. State-selected CIS spectra highlighted the importance of the autoionizing contribution to the production of almost all ionized states of 1,1-C2H2F2 observed in this work. Several peculiarities of the vibrationally resolved CIS spectra are analysed.

Electronic structure and photoionization dissociation studies of chlorocarbonyl trifluoromethanesulfonate, CF3SO3C(O)Cl

Chlorocarbonyl trifluoromethanesulfonate, CF3SO3C(O)Cl, was prepared by heterogeneous reaction of gaseous ClC(O)SCl with CF3SO3Ag. The electronic structure and photoionization dissociation were investigated by HeI photoelectron spectroscopy (PES) and photoionization mass spectroscopy (PIMS). The assignments of the bands in the PES were reasonably supported by previous studies on analogous molecules, as well as the outer-valence Green’s function (OVGF) calculations. The experimental first vertical ionization potential of CF3SO3C(O)Cl was determined to be 12.36eV, which was assigned to the ionization mainly from the oxygen lone pair orbital. It shows three peaks: ClCO+ (63, 65), CF3+ (69) and CF3SO2+ (133) in the spectrum of PIMS, with the dominant features being the ClCO+ and CF3+ peaks. According to the calculated bond dissociation energies, the dissociation process was also discussed.

Electronic Structure and Conformation Properties of Halogen -Substituted Acetyl Acrylic Anhydrides, CX3C(O)OC(O)CH═CH2 (X = H, F, or Cl)

Acetyl acrylic anhydride (CH(3)C(O)OC(O)CHCH(2)) and its halogen-substituted derivatives (CF(3)C(O)OC(O)CHCH(2) and CCl(3)C(O)OC(O)CHCH(2)) were prepared by the heterogeneous reaction of gaseous CH(2)═CHC(O)Cl with CX(3)C(O)OAg (X = H, F, or Cl). The molecular conformations and electronic structure of these three compounds were investigated by HeI photoelectron spectroscopy, photoionization mass spectroscopy, FT-IR, and theoretical calculations. They were theoretically predicted to prefer the [ss-c] conformation, with each C═O bond syn with respect to the opposite O-C bond and the C═C bond in cis orientation to the adjacent C═O bond. The experimental first vertical ionization potential for CH(3)C(O)OC(O)CHCH(2), CF(3)C(O)OC(O)CHCH(2), and CCl(3)C(O)OC(O)CHCH(2) was determined to be 10.91, 11.42, and 11.07 eV, respectively. In this study, the rule of the conformation properties of anhydride XC(O)OC(O)Y was improved by analyzing the different conformations of anhydrides with various substitutes.

Electronic structure of two catalytically important hafnocenes

The electronic structures of trichloro[(1,2,3,3a,7a-η)-1H-inden-1-yl]-hafnium and bis(cyclopentadienyl)hafnium dichloride have been investigated by HeI and HeII UV photoelectron spectroscopy and DFT/OVGF calculations. The chlorine lone pair ionization energies are reduced considerably on going from HfCl4 to metallocene hafnium chlorides. The electronic structure results have been related to the mechanism of olefin polymerization catalyzed by hafnocenes.

Outermost and Inner-Shell Electronic Properties of ClC(O)SCH2CH3 Studied Using HeI Photoelectron Spectroscopy and Synchrotron Radiation

A study of valence electronic properties of S-ethyl chlorothioformate (S-ethyl chloromethanethioate), ClC(O)SCH(2)CH(3), using HeI photoelectron spectra (PES) and synchrotron radiation is presented. Moreover, the photon impact excitation and dissociation dynamics of ClC(O)SCH(2)CH(3) excited at the S 2p and Cl 2p levels are elucidated by analyzing the total ion yield (TIY) spectra and time-of-flight mass spectra acquired in multicoincidence mode [photoelectron-photoion coincidence (PEPICO) and photoelectron-photoion-photoion coincidence (PEPIPICO)]. The HeI photoelectron spectrum is dominated by features associated with lone-pair electrons from the ClC(O)S- group, the HOMO at 9.84 eV being assigned to the n(π)(S) sulfur lone-pair orbital. Whereas the formation of C(2)H(5)(+) ion dominates the fragmentation in the valence energy region, the most abundant ion formed in both the S and Cl 2p energy ranges is C(2)H(3)(+). Comparison with related XC(O)SR (X = H, F, Cl and R = -CH(3), -C(2)H(5)) species reveals the impact of the alkyl chain on the photodissociation behavior of S-alkyl (halo)thioformates.

Molecular and Electronic Structure of δ-Valerothiolactone

The crystal structure of the six-member heterocyclic δ-valerothiolactone (1-thiocycloalkan-2-one) compound has been determined by X-ray diffraction at low temperature, revealing that its skeleton adopts a half-chair conformation. The conformation around the thioester group is almost planar with an anti orientation of the C=O double bond with respect the S-C single bond [C(2)-S(1)-C(6)-O(1) = 176.26(8)°]. The skeletal parameters, especially valence angles [∠C5-C6-S = 121.19(6)°, ∠O=C6-C5 = 122.25(8)°, ∠C6-S-C2 = 106.80(4)°], differ from those typically found in acyclic thioester compounds, symptomatic of the presence of strain effects. The conventional ring strain energy was determined to be 7.5 kcal/mol at the MP2/6-311++G(d,p) level of calculation within the hyperhomodesmotic model approximation. Moreover, the valence electronic structure was investigated by HeI photoelectron spectroscopy assisted by quantum chemical calculations at the OVGF/6-311++G(d,p) level of theory. The first three bands at 9.35, 9.50, and 11.53 eV denote ionizations related with the n(S), n(O), and π(C=O) orbitals, respectively, demonstrating the importance of the -SC(O)- group in the outermost electronic properties.

On the biological activity of drug molecules: Busulfan and nabumetone

The electronic structures of drug molecules busulfan (BSU) and nabumetone (NAB) have been investigated by HeI and HeII UV photoelectron spectroscopy (UPS), quantum chemical calculations and virtual docking studies. Their biological activities are discussed in the framework of their electronic and molecular structures, reactivity and drug-enzyme binding.

Electronic structure of two phosphorus compounds

The electronic structures of tri-2-furanyl-phosphine ( I) and 1,2-bis(dimethoxyphosphoryl)benzene ( II) have been investigated by HeI and HeII UV photoelectron spectroscopy (UPS) and quantum chemical calculations. Their electronic structures are discussed in the framework of their chemical properties and practical applications with special reference to the extent of intramolecular interactions. We have also rationalized the observed increased shielding of phosphorus in 31P NMR spectra of TFP.