Photoelectron Spectra of Azabenzenes and Azanaphthalenes: I. Pyridine,diazines, s-triazine and s-tetrazine

The experimental and theoretical basis of a recently proposed reassignment of the bands in the PE. spectra of pyridine, pyridazine, pyrimidine and pyrazine is discussed in detail. A characteristic feature of the derived orbital sequence is that it takes the ‘through-space’ and ‘through-bond’ interaction between the ‘lone pair’ basis orbitals explicitly into account. A simple parametrization of the orbital energies, based on HMO-type models for the π-orbitals and for the ‘lone pair’ linear combinations, yields excellent agreement with the observed band positions in the PE. spectra of s-triazine and s-tetrazine. Our new assignment is compared to those proposed previously.     

Photoelectron Spectra of Azabenzenes and Azanaphthalenes: III. The orbital sequence in methyl- and trimethylsilyl-substituted pyridines

The ionization potentials of methyl-, t-butyl- and trimethylsilyl-substituted pyridines have been determined by high-resolution photoelectron spectroscopy. The results are discussed in terms of destabilizing inductive and stabilizing conjugative effects of the substituents, and have been parametrized on the basis of a HMO-type perturbation treatment. Our data are in accord with the idea that the topmost occupied orbital in pyridine is a ‘lone pair’ orbital.     

High-Resolution Threshold Photoelectron Spectroscopy by Vacuum Ultraviolet Laser Velocity-Map-Imaging Method

We have obtained the high-resolution threshold photoelectron (TPE) spectra of chlorobenzene C₆H₅Cl (X¹A₁), propargyl radical C₃H₃ (X²B₁), and allyl radical C₃H₅ (X²A₁) by employing the vacuum ultraviolet (VUV) laser velocity-map-imaging-TPE (VUV-VMI-TPE) method. The photoelectron energy resolution of 1-2 cm^-1 observed for the VUV-VMI-TPE method is comparable to that achieved in VUV laser pulsed-field ionization-photoelectron (VUV-PFI-PE) measurements. Similar to VUV-PFI-PE measurements, the energy resolutions for VUV-VMI-photoelectron (VUV-VMI-PE) and VUV-VMI-TPE measurements are found to depend on the dc electric field F in V/cm used at the photoionization region for electron extraction. The decrease of the ionization thresholds of C₆H₅Cl and C₃H₃ observed as a function of F shows that the Stark shift correction for VUV-VMI-TPE measurements is governed by the formula -3.1√F in cm^-1, which is half of the classical prediction of -6.1√F in cm^-1.} We have also measured the VUV-VMI-PE spectra of C₆H₅Cl and C₃H₅ at VUV energies near their ionization thresholds. The cationic vibrational bands observed in the VUV-VMI-PE measurements were assigned to be the vibrational progression, nv₇⁺ (n=0-3), for C₃H₅⁺. The higher experimental sensitivity and similar energy resolutions achieved in VUV-VMI-TPE compared to VUV-PFI-PE measurements make the VUV-VMI-TPE method an excellent alternative for high-resolution VUV-PFI-PE measurements.     

Spectroscopy of Ethylenedione and Ethynediolide: A Reinvestigation

In an effort to characterize the electronic states of ethylenedione, OCCO, photoelectron‐photofragment coincidence (PPC) spectroscopy was applied to measure anions at m/z 56 and 57 using a pulsed discharge of glyoxal vapor and N₂O. PPC measurements at a photon energy of 3.20 eV yield photoelectron spectra in coincidence with either neutral photofragments or stable neutral products. The measurements showed that primarily stable neutral products were formed, with photoelectron spectra consistent with the oxyallyl diradical, C₃H₄O, and acetone enolate radical, C₃H₅O. The spectra were also found to have features nearly identical to those reported for OCCO and HOCCO by Sanov and co‐workers. The stability of the neutral products, as well as an examination of spectra reported for the oxyallyl anion and acetone enolate show that the previous assignments of OCCO and HOCCO are in error, and are instead attributed here to the oxyallyl diradical, C₃H₄O, and the acetone enolate radical, C₃H₅O.     

Conformational Analysis by Photoelectron Spectroscopy

The conformation of organic molecules may be determined by means of photoelectron (PE) spectroscopy if there are orbital interactions present which depend on a dihedral angle. Straightforward application of the method requires that all ionization bands of interest can be assigned unambiguously and that inductive effects and secondary orbital interactions do not occur or can be accounted for appropriately. In many cases, this method complements conventional methods of conformational analysis. PE conformational analysis is particularly suited to compounds containing vicinal lone pairs or π systems.     

ChemInform Abstract: Photoelectron Spectroscopy of BH- 3.

The photoelectron spectra of BH₃^- and BD₃^- are studied and the electron affinities of borane are determined to be EA(BH3) = 0.038 eV and EA(BD3) = 0.027 eV.     

Analytical Aspects of Photoelectron Spectroscopy

Photoelectron spectroscopy is a new technique for experimentally measuring the binding energies of electrons in molecules. The basic principles of the method are outlined and simple guidelines for the interpretation of u.v.-excited photoelectron spectra are laid down. The analytical potential and possible development of the method are briefly surveyed.     

Photoelectron Spectroscopy of peri-Amino Naphthalenes

The He I photoelectron spectra of peri-amino and dimethylamino naphthalenes are presented. The differences in the ionization energies of the π-bands are interpreted by separation of the perturbation of the amino substituent into an inductive destabilization and conjugative stabilization. This affords the assignment of the photoelectron bands of ionization energies below 11 eV and an estimation of the dihedral angle in the peri-dimethylamino derivatives. The data on the peri-amino naphthalenes indicate some angular distortion in contrast to 2-aminonaphthalene.     

苯并噻唑衍生物的气相HeI紫外光电子能谱(UPS)及量子化学研究

对苯并噻唑系列衍生物的气相HeI紫外光电子能谱(UPS)进行了研究．首次报道 了五种化合物的紫外光电子能谱，利用Gaussian94从头算的量子化学计算方法对其 进行了计算，并结合计算结果对各个分子体系的谱图进行了指认．研究结果表明： 分子的电离能受取代基性质的影响，取代基的给电子能力越大，体系的共轭效应越 强，电离能就越低．对苯并噻唑衍生物而言，6-位取代基对电离能的影响大于2-位 取代基的影响．     

Threshold Photoelectron Spectroscopy of IO and HOI

Iodine oxides appear as reactive intermediates in atmospheric chemistry. Here, we investigate IO and HOI by mass-selective threshold photoelectron spectroscopy (ms-TPES), using synchrotron radiation. IO and HOI are generated by photolyzing iodine in the presence of ozone. For both molecules, accurate ionization energies are determined, 9.71±0.02 eV for IO and 9.79±0.02 eV for HOI. The strong spin-spin interaction in the ³Σ⁻ ground state of IO⁺ leads to an energy splitting into the Ω=0 and Ω=±1 sublevels. Upon ionization, the I−O bond shortens significantly in both molecules; thus, a vibrational progression, assigned to the I−O stretch, is apparent in both spectra.     

负离子光电子能谱技术发展及应用

负离子光电子能谱已经成为探索光谱和化学动力学基础问题的最为重要的技术之一。本文简要介绍了负离子光电子能谱的发展历史,回顾了负离子光电子能谱发展过程中的几种主要技术,包括为了提高分辨率而开发出的零动能能谱和慢电子速度成像技术以及为在气相条件下研究多电荷负离子及其对应中性分子电子特性而开发的电喷雾源与负离子光电子能谱结合的技术。随后介绍其在锕系元素及化合物、含铍化合物的电子结构及成键特征研究中的应用及进展。     

Pyridine Dimers and Their Low-Temperature Isomerization: A High-Resolution Matrix-Isolation Spectroscopy Study

The bonding between two neutral aromatic compounds, especially small ones, has been controversially debated in the last decades, and terms like “π-stacking” had to be revised. Surprisingly, despite of many experimental and computational work, there is still no clear consensus about the structure of and the bonding in the pyridine dimer. In this work, for different isomeric forms of the pyridine dimer, the structures and bonding were elucidated by combining high-resolution matrix-isolation spectroscopic results with quantum-chemical calculations. High-resolution IR spectra of Ne matrices at 4 K containing pyridine were recorded for different concentrations and upon annealing to 10 and 12 K, relying on three isotopologues of pyridine. The spectra show the presence of hydrogen-bonded, T-shaped, and stacked forms of weakly-bound pyridine dimers. Among these, the hydrogen-bonded isomer is identified as the lowest-energy form. The results provide for the first time conclusive information about the interaction between two pyridine dimers.     

Probing the Cellulose-Ionic Liquids Interaction by X-ray Photoelectron Spectroscopy

X-ray photoelectron spectroscopy is used as a probe to demonstrate the interaction between cellulose and 1-butyl-3-methylimidazolium chloride. The fitting models of C 1s spectra for the ionic liquid, cellulose and cellulose containing solutions are developed. The measured binding energy of C² 1s component is used to indicate the ionic liquid-cellulose interaction. In the case of the cellulose containing solution, due to the weaker charge-transfer effect between hydrophilic groups of cellulose and the imidazolium cation, the C² atom is in a more electropositive environment and thus exhibits higher binding energy.     

Photoelectron Photoion Coincidence Spectroscopy of Biradicals

The electronic structure of biradicals is characterized by the presence of two unpaired electrons in degenerate or near-degenerate molecular orbitals. In particular, some of the most relevant species are highly reactive, difficult to generate cleanly and can only be studied in the gas phase or in matrices. Unveiling their electronic structure is, however, of paramount interest to understand their chemistry. Photoelectron photoion coincidence (PEPICO) spectroscopy is an excellent approach to explore the electronic states of biradicals, because it enables a direct correlation between the detected ions and electrons. This permits to extract unique vibrationally resolved photoion mass-selected threshold photoelectron spectra (ms-TPES) to obtain insight in the electronic structure of both the neutral and the cation. In this review we highlight most recent advances on the spectroscopy of biradicals and biradicaloids, utilizing PEPICO spectroscopy and vacuum ultraviolet (VUV) synchrotron radiation.     

RE—Al—Zr—C—N多元渗的XPS研究

用气相法对45钢表面进行RE－Al-Zr-C-N多元渗，通过X射线光电子能谱（XPS）给出了该体系中各元素的结合能位置，分析了它们的存在状态，同时用扫描电镜－能谱进行了形貌分析，元素分析等，证实RE，Al,Zr,C,N渗入到了金属表层，在共渗中发现微量稀土元素对铝的活化催渗作用大于其对锆的作用，进一步证实了对氮的作用亦优于对碳的活化催渗作用。     

一些钼络合物的X光电子能谱

本文研究了一些钼络合物的X光电子能谱,测定了钼3d电子的结合能(E_b),并讨论了钼的氧化态和桥连原子对此的影响。