Derek Jones

Experimental and theoretical study of intense shake-up structures in the XPS spectra of nitrobenzenes and nitrosobenzenes

Abstract The N 1s and O 1s energy regions of the XPS spectra of para-substituted nitrobenzenes and nitrobenzenes [ p -X-C 6 H 4 -NO 2 : X = H, OH, OCH 3 , NH 2 and N(CH 3 ) 2 ; p -X-C 6 H 4 -NO: X = H, Cl, OCH 3 and N(CH 3 ) 2 ] present, close to the main lines, one (NO 2 -derivatives) or two (NO-derivatives) shake-up peaks whose intensity increases steadily with the electron-releasing ability of the substituent. All main energy and intensity trends experimentally observed are correctly reproduced by CNDO/S-Cl calculations, both within given compounds and along the two series. The origin of the satellites and the differences noted between the two series are discussed. The present experimental and theoretical results are in complete agreement with our qualitative explanation of the multi-peak structures previously observed in nitroanilines and other polar aromatic nitro-derivatives.

Influence of the oxy, aza and thio groups on the electron affinities of carbonyl compounds studied by means of ETS

Abstract The attachment energies (AEs) related to temporary electron capture into the empty π* MOs of some cyclic carbonyl and dicarbonyl derivatives have been measured by ETS. The AE values have been found to depend on the nature of the atom or group X bonded to the carbonyl group(s). Changing X from CH 2 to O and NR results in a large (1–2 eV) destabilization of appropriate MOs, whereas this effect is not observed for X = S. These findings have been discussed on the basis of hetero-atom lone-pair energy, bond distances and involvement in bonding of low-lying empty orbitals. The AE data are consistent with a large lone-pair -π co * charge-transfer interaction when X = O and NR and with a reduction of this effect and 3d-π co * mixing when X = S.

ESCA and UPS Spectra of Nitronaphthylamines. Shake-up structures, relaxation effects and through-space interaction between the two substituents

The X-ray and UV photoelectron spectra of several nitronaphthylamine isomers are reported. In some cases, the nitro N1s signal is accompanied by an intense satellite band 1.5-2.0 eV from the main photoline having 60-150% of its intensity; also in the corresponding O1s energy region a satellite band is present having a larger energy separation from the main peak (2.0-2.35 eV) and smaller relative intensity (Ish = 10-30%). The difference between the ionization energy values of the nitro and amino N1s signal (?N1s) is found to follow the same trend found for the intensity of the satellite and log , the optical absorption coefficient of the HOMO-LUMO charge-transfer (CT) transition. These satellites are ascribed to a shake-up process involving a CT transition from the naphthylamine part of the molecule towards a ?* MO localized on the nitro group on the basis of a simple model we have previously proposed for nitroanilines and other aromatic derivatives. The trend of ?N1s is thought to derive mainly from a greater interatomic valence band relaxation accompanying nitro N1s ionization than amino N1s ionization, rather than from variation of the ground state charges at the two nitrogen atoms. The UPS spectra indicate that there is no sizeable variation of the ground state mesomeric interaction between the two substituents on changing the position of the nitro group, and suggest mutual interaction of the two substituents when they are adjacent.

Shake-up transitions in the XPS spectra of benzonitriles and benzaldehydes

Abstract Shake-up peaks of low-to-moderate intensity accompany core ionisation at the acceptor group of some parasubstituted benzonitriles, X C6 H4 CN [X = H, OCH3, NH2 and N(CH3)2] and benzaldehydes X C6H4 CHO [X = H and N(CH3)2]. Their main energy and intensity trends are reproduced by CNDO/S-CI calculations. The model previously proposed to explain the intense shake-up structure of nitrobenzenes and nitrosobenzenes applies equally well to the present compounds. The trends observed between and along series of compounds are discussed. In benzonitriles the dominant factor determining the energy and intensity of the main satellite line is the energy of the HOMO.

Intense shake-up satellites in the XPS spectra of planar and sterically hindered N-piperidyl-nitrobenzenes and -nitrothiophens

Abstract The shake-up satellites present in the O 1s and N 1s energy regions of the XPS spectra of the planar 4-N-piperidyl-nitrobenzene ( 1 ) and 2-N-piperidyl-5-nitrothiophen ( 3 ), and of the sterically hindered 2-N-piperidyl-nitrobenzene ( 2 ), 2-N-piperidyl-3-nitrothiophen ( 4 ) and 3-N-piperidyl-2-nitrothiophen ( 5 ) and, for comparison, of 2-bromo-3-nitrothiophen ( 6 ) have been analyzed with the help of CNDO/S CI calculations. The spectra of the planar derivatives closely resemble these of the related compounds previously analysed, the main satellites deriving from the transition between the highest occupied molecular orbital (HOMO, localized at the donor-ring moiety) towards the lowest unoccupied one (LUMO, localized at the nitro group). Calculations indicate that in the ortho derivatives new relaxation processes are allowed upon N 1s /NO 2 ionization. In 2 , where the angle of rotation θ is closer to 90° than 60°, the NR 2 lone-pair orbital relaxes through space towards the core-ionized N/NO 2 atom. In 4 and 5 , where 45° ⩽ θ ⩽ 60°, both through-ring and through-space relaxations are present. The assignment of the main N 1s /NO 2 line in 1 is discussed.

Photoelectron (He(I), He(II) and X-ray) spectroscopy of γ-pyrone and its related sulphur derivatives: valence and core ionization energies and shake-up satellites

Abstract The photoelectron He(I) and He(II) spectra of 4H-pyran-4-one ( 1 ), 4H-thiopyran-4-one ( 2 ), 4H-pyran-4-thione ( 3 ) and 4H-thiopyran-4-thione ( 4 ) are reported. The assignments are based on experimental evidence, taking into account the results of theoretical calculations. The outermost orbital sequences proposed (X = O, S) are n X (σ), 3 b 1 (π), 1 a 2 (π) for 1 , 2 and 4 ; and 3 b 1 (π), n X (σ) and 1 a 2 (π) for 3 . The shifts of the core-ionization energy values for 1–4 are ascribed to a drift of π-charge from the intracyclic heteroatom towards the carbonyl or thiocarbonyl group. Low-energy shake-up satellites (up to 25% with respect to the main line) are observed in the various energy regions of the XPS spectra. They are qualitatively reproduced by CNDO/2 calculations. The most important satellites derive from the transition in the ion corresponding to the 3 b 1 (π) → 4 b 1 (π*) transition in the UV-visible spectra of the neutral molecules. Charge rearrangements accompanying this transition lead to charge depletion of the core-ionized atom.

Electron attachment to indole and related molecules

Gas-phase formation of temporary negative ion states via resonance attachment of low-energy (0-6 eV) electrons into vacant molecular orbitals of indoline (I), indene (II), indole (III), 2-methylen-1,3,3-trimethylindoline (IV), and 2,3,3-trimethyl-indolenine (V) was investigated for the first time by electron transmission spectroscopy (ETS). The description of their empty-level structures was supported by density functional theory and Hartree-Fock calculations, using empirically calibrated linear equations to scale the calculated virtual orbital energies. Dissociative electron attachment spectroscopy (DEAS) was used to measure the fragment anion yields generated through dissociative decay channels of the parent molecular anions of compounds I-V, detected with a mass filter as a function of the incident electron energy in the 0-14 eV energy range. The vertical and adiabatic electron affinities were evaluated at the B3LYP∕6-31+G(d) level as the anion∕neutral total energy difference. The same theoretical method is also used for evaluation of the thermodynamic energy thresholds for production of the negative fragments observed in the DEA spectra. The loss of a hydrogen atom from the parent molecular anion ([M-H](-)) provides the most intense signal in compounds I-IV. The gas-phase DEAS data can provide support for biochemical reaction mechanisms in vivo involving initial hydrogen abstraction from the nitrogen atom of the indole moiety, present in a variety of biologically important molecules.

X-ray photoelectron spectra of 2-propenal and related compounds

Abstract Energy and intensity variations of the shake-up satellites accompanying core-ionization at the acceptor group CO in the XPS spectra of 3-dimethylamino-2-propenal (2) compared to 2-propenal (1) have been ascribed to an increase of π-electron polarizability. The presence in the spectrum of 2 of a shake-up peak in the donor (N 1s ) region, has been related to the pronounced ground state charge-transfer interaction. A comparison of the shake-up structures of 2-propenamide (3) with those of 1, 2 and related compounds, shows that intensity reduction can be related to distortion from planarity of the molecular sekeleton.

On the structure and spectroscopic properties of the cis- and trans-isomers of cyclen- and cyclam-glyoxal

Abstract The equilibrium structures of the cis- and trans-isomeric derivatives of the cyclen and cyclam condensation products with glyoxal were investigated with the density functional theory (DFT) model B3LYP/6-31G(d,p). According to calculations, the trans-fused condensation product is more stable than the cis product by 2xa0kcalxa0mol−1 in the case of cyclam. For cyclen, the stability order is instead inverted, the cis-fusion being much more preferred by 9.8xa0kcalxa0mol−1. The 13C NMR chemical shifts were recorded and analyzed by means of continuous set of gauge transformations (CSGT) calculations performed with the HF-B3LYP/6-311+G(2d,p) hybrid functional model. The He(I) photoelectron spectra were measured and interpreted by means of ab initio outer valence Green function (OVGF) calculations, which give a consistent, overall description of the uppermost bands, associated with the four nitrogen lone pair orbitals.

Theoretical study of the molecular structure and spectroscopic properties of 1,7;3,5-dimethylene-cis-1,3,5,7-tetraazadecalin

Abstract The equilibrium structure of 1,7;3,5-dimethylene- cis -1,3,5,7-tetraazadecalin was fully optimized at the MP2/6-31+G(d) ab initio level of theory. The NMR 13 C and 15 N chemical shifts were analyzed by means of ab initio CSGT (continuous set of gauge transformations) calculations performed with the HF-B3LYP/6-311+G(2d,p) hybrid functional model. The He(I) photoelectron spectrum was measured and interpreted by means of ab initio OVGF (outer valence Green function) calculations, which give an overall consistent reproduction of the energies and splittings of the uppermost bands. This heterocyclic molecule was found to be characterized by two moderately interacting groups of two nitrogen lone pairs each, outwardly directed in the small cage of C 2 symmetry.