He (I) and He (II) photoelectron spectra of ozone

The he I (21.2 eV) and He II (40.8 eV) photoelectron spectra of ozone have been recorded under high resolution. Ionization potentials are identified at 12.75 eV, 13.02 eV, 13.57 eV, and two broad bands are centered at 17.7 eV and 20.1 eV. The experimental results and the orbital assignment are not completely in accord with those given recently in the literature.     

Photoionization cross sections: He I and He II photoelectron spectra of saturated three-membered rings

The relative band intensities in the He I and He II photoelectron spectra of cyclopropane, oxirane, and thirane are interpreted by means of a recent theoretical approach. For each compound, the assignment of the two bands in the 15–18 eV range derived from our intensity arguments is opposite to the sequence of the respective ab initio eigenvalues.     

Hei and heii spectra of 3-halopyridines

The ultraviolet photoelectron spectra (UPS) of 3-fluoro-, 3- chloro-, 3-bromo- and 3- iodopyridine were recorded and interpreted using a composite-molecule model. The sequence of the four lowest ionization energies for 3-fluoro- and 3-chloropyridine is: π₃ (1a₂) < n_N (11a₁)ππ₂ (2b₁)π∼_pyr (7b₂), whereas for 3-bromo- and 3-iodopyridine the assignment is: π₃ (1a₂) - π_xπn_N (11a₁)πσ_x π₂ (2b₁) (where X represents a bromine or iodine lone-pair). Comparison of the HeI and HeII band intensities and correlations with the UPS assignment of the 2-halopyridines confirm this sequence. However, ab initio calculations using the STO-3G*//STO-3G* and 6–31G**//STO-3G* models do not agree with either the composite-molecule model, simple UPS correlations and HeI/HeII cross-section ratios. For 3-fluoropyridine, the HAM/3 model was in agreement with the proposed assignment.     

New synthesis routes to 2-halopyridines. II. 2-bromopyridine

The use of bromine chloride (equilibrium mixture) in substitution reactions has been extended to heterocyclic substrates. The vapor phase bromination of pyridine (I) with bromine chloride at temperatures as low as 375° (carbon tetrachloride diluent) gave the following product distribution: 2-bromopyridine (IV) (75%) > 2-chloropyridine (VI) (21%) > 3-bromopyridine (II) (2.0%) ? 2,6-dibromopyridine (VI) (1.5%). In contrast, when bromine was employed in place of bromine chloride (450°; carbon tetrachloride diluent), product orientation was significantly altered to give nearly equal quantities of 3-bromopyridine (II) (17%) and 2-bromopyridine (IV) (22.7%).     

He I and Ne I photoelectron spectra of dichloro- and dibromomalononitrile

He I and Ne I photoelectron spectra are reported for the densely populated valence regions of gaseous malononitrile, H₂C(CN)₂, dichloromalononitrile, Cl₂C(CN)₂, and dibromomalononitrile, Br₂C(CN)₂. A minor reassessment of the H₂C(CN)₂ assignments is extended to permit plausible assignments for the previously unreported dihalodicyano species. Semiempirical calculations, HAM/3 and MNDO for H₂C(CN)₂, and MNDO for the X₂C(CN)₂ molecules, are shown to be of limited value for the location of strongly localised nitrogen orbitals.     

New synthesis routes to 2-halopyridines. I. 2-chloropyridine

In contrast to the wide variety of products previously reported from the non-photolytic liquid or vapor phase chlorination of pyridine (I), it has been demonstrated that the corresponding photochemical chlorination of I in carbon tetrachloride under reflux conditions gave 2-chloropyridine (IV) in 62–78 percent yield.     

He I photoelectron spectra of some camphor derivatives

He I photoelectron spectra of several camphor derivatives have been measured and assigned.     

He(I) and He(II) photoelectron spectra of some mixed sandwich compounds of titanium,zirconium and hafnium

The He(I) and He(II) photoelectron spectra are reported for two series of transition metal mixed sandwich complexes of general formula L_aML_b (M = Ti, L_a = η⁵-C₅H₅, η⁵-CH₃C₅H₄, η⁵-C₅(CH₃)₅; M = Zr, Hf, L_a = η⁵-C₅(CH₃)₅; L_b = η⁷-C₇H₇ (series I); M = Ti, L_a = η⁵-CH₃C₅H₄, η⁵-C₅(CH₃)₅; M = Zr, L_a = η⁵-C₅(CH₃)₅; L_b = η⁸-C₈H₈ (series II)). Assignments were made of the metal d, cyclopentadienyl and carbocyclic π orbitals on the basis of He(I)/He(II) intensity ratios and shift effects and by comparison with UP data for related compounds. For series I no influence of the central metal upon the IEs of the highest occupied molecular orbital e₂ was observed. The IE of the non-bonding metal d_z2 orbital of Ti or Zr (5.28 and 4.70 eV, respectively) in the complexes of series II (L_a = η⁵-C₅(CH₃)₅) is very low.     

Experimental and theoretical investigations of the He...I2 rovibronic spectra in the I2 B-X, 20-0 region

The laser-induced fluorescence and action spectra of I2 in a helium supersonic expansion have been recorded in the I2 B-X, 20-0 region. Two features are identified within the spectra. The lower-energy feature arises from transitions between states that are localized in a T-shaped conformation on both the X- and B-state potentials. The higher-energy feature reflects transitions from states that are localized in a linear conformation on the X state to states that have energies that are larger than the barrier for free rotation of the rare gas atom about the I2 molecule on the B-state potential. Ground-state binding energies of 16.6(6) and 16.3(6) cm-1 were determined for the T-shaped and linear conformers, respectively. These spectra are compared to those calculated using the experimentally determined rotational temperatures. Based on the agreement between the experimental and calculated spectra, the binding energies of the J'=0 states with 0 and 2-6 quanta of excitation in the He...I2 bending mode on the B state were determined. Several models for the B-state potential were used to investigate the origins of the shape of the contour of the higher-energy feature in the spectra for He...I2 and He...Br2. The shape of the contours was found to be relatively insensitive to the choice of potential. This leads us to believe that the spectra of these systems are relatively insensitive to the parameters of the B-state potential energy surface and are more sensitive to properties of the halogen molecule.     

Isonitrile ligand properties as studied by He I/He II photoelectron spectroscopy

A new series of isonitrile-substituted cobalt tricarbonyl nitrosyl (Co(CO)₂(NO)CNR, R = Me, Et, ⁿPr, ⁱPr, ⁿBu, ⁿPe, CH₂Si(CH₃)₃) has been synthesized, and their He I ultraviolet photoelectron spectra are reported. The assignment of the bands in the low energy part of the spectra was performed with the aid of DFT calculations. The first vertical ionization energies of the complexes were found to be 7.73 (CNMe), 7.58 (CNEt), 7.59 (CNⁿPr), 7.70 (CNⁿBu), 7.67 (CNⁿPe), 7.77 (CNⁱPr), and 7.54 ± 0.03 eV (CNCH₂Si(CH₃)₃). In the case of ⁿPr- and CH₂Si(CH₃)₃- substitutions, He II photoelectron spectra were also recorded. The relative importance of electronic and steric effects of the isonitrile ligands, as a function of the size of group –R, is discussed.     

Nucleophilic substitution in 2-nitro-3-halopyridines

Nucleophilic substitution occurs in the 2 or 3 position in 2-nitro-3-halopyridines depending on the nature of the halogen and the substituting agent. A series of new 2,3-substituted pyridines were obtained as a result of the reactions.     

He I photoelectron spectra of [3]-ferrocenophane and its 7-oxa derivative

He I photoelectron spectra of [3]-ferrocenophane and 6,8-dimethyl-7-oxa-[3]-ferrocenophane have been measured. In comparison with ferrocene the energy gap between ²E′₂(a′₁²e′₂³) and ²A′₁(a′₁¹e′₂⁴) is decreased to 0.28 and 0.22 eV due to the destabilization of the a′₁(d)-level originating in its more pronounced mixing with ligand orbitals. The increase of photoionization cross section of the a′₁(d)-level in the 6,8-dimethyl-7-oxa-[3]-ferrocenophane spectrum supports this interpretation. The band shapes and ionization potentials of ligand π-levels are strongly influenced by the hydrocarbon bridge.     

New synthesis routes to 2-halopyridines. III. 2-fluoropyridine

The solvent-free fluorination of 2-chloropyridine (III) with alkali metal fluorides and bifluorides was investigated. While complete degradation occurred with potassium fluoride at 315°, the use of potassium bifluoride under identical conditions provided a 74% yield of 2-fluoro-pyridine (II). Sodium bifluoride gave only a 3.5% yield of the desired product. These results are discussed in the light of: activation of the substrate, properties of the fluorinating agents, and the stability of 2-fluoropyridine.     

He I (584 Å) photoelectron spectra and photoionization cross sections of atomic chlorine and bromine

Well-resolved He I photoelectron spectra of atomic chlorine and bromine have been obtained without serious background electrons, giving rise to relative photoelectron intensities associated with differential photoionization cross sections at an angle of 90° with respect to the incident 584 Å radiation.     

Penning electron spectra from ionization of hydrogen atoms by He(2S) and He(2S) metastables

Separate Penning electron spectra were measured resulting from the ionization of H atoms by He(2¹S) and He(2³S) metastables in thermal collisions. From these results potential parameters of the diatomics He(2¹S)-H(²S) (²Σ) and He(2³S)-H(²S) (²Σ) as well as the cross-section ratio σ(singlet)/σ(triplet) are derived.     

The role of the He I and He II metastables in the population of the Sn II,Sn III and Sn IV ion levels

On the basis of the temporal evolutions of the singly, doubly and triply ionized tin (Sn II, Sn III and Sn IV, respectively) spectral line intensities, in the pulsed helium and nitrogen plasmas, the important role of the He I and He II metastables has been observed in the Sn II, Sn III and Sn IV ionization and population processes. According to these processes, one can expect realization of several laser levels in the Sn II (11.07, 11.20, 12.44 and 13.11 eV), Sn III (15.91, 17.82, 19.13 and 20.19 eV) and Sn IV (20.51 eV) spectra. The modified version of the linear, low-pressure, pulsed arc was used as a plasma source operated in helium with tin atoms, as impurities, evaporated from tin cylindrical plates located in the homogenous part of the discharge tube. This plasma source provides good conditions for a generation of the Sn III, Sn IV and Sn V ions at relatively low electron temperatures (below 18,000 K) providing low background radiation around the intense Sn IV and Sn III spectral lines in the helium plasma. The 222.613 ± 0.0005 nm Sn IV line, not observed up to now, has been identified. The marked, but not classified 243.688 nm Sn spectral line is sorted by ionization stages. The shapes of Sn III and Sn IV lines, ranged between 207 nm and 307 nm, have been obtained. At a 17,500 K electron temperature and 1.07 × 10²³ m^− 3 electron density the Stark broadening was found as the dominant mechanism in the mentioned lines broadening. The measured Stark widths of the prominent nine Sn IV and seven Sn III lines are the first data in the literature. The Stark widths of the intense 229.913 nm and 288.766 nm Sn IV lines can be used for the plasma electron density and temperature diagnostics purposes.     

He(I) photoelecteonic spectra of organic compounds with a mercury atom attached to AN sp2-hybeidized carbon

Conclusion The He (I) photoelectronic spectra of some organomercury compounds of the vinyl type were studied and the nature of the electronic effects in these molecules was discussed.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2831–2834, December, 1981.     

The surface activity of p-aminotriphenylmethane dyes in organic solvents - He(I) photoelectron spectra

At 0.23 M, the superficial layer of a solution of malachite green hydroxide or of brilliant green hydroxide in hydroxy-propionitrile consists entirely of the dye (as measured by He (I) photoelectron spectroscopy). This surface activity is weak or non-existent in the chloride and oxalate of malachite green, in some related dyes like brilliant green bisulphate and in the hydroxides and salts of both p-rosaniline and crystal violet.