Photoelectron spectroscopic study of simple hydrogen-bonded dimers. II. The methanol dimer

HeI photoelectron spectra of a supersonic jet of methanol vapor have been obtained by using the temperature-controlled supersonic nozzle beam photoelectron spectrometer recently constructed in our laboratory. A HeI spectrum attributable to the methanol dimer (CH₃OH)₂ has been deduced by spectrum stripping. The first ten vertical ionization energies and the first adiabatic ionization energy of (CH₃OH)₂ have been determined from the stripped spectrum. Ab initio SCF MO calculations of ionization energies have also been carried out for (CH₃OH)₂ on the basis of Koopmans' theorem. The lower bound of the dissociation energy of (CH₃OH)₂⁺ has been estimated to be 1.2 ± 0.2 eV from the adiabatic ionization energies of the monomer and dimer. The equilibrium structure of (CH₃OH)₂ is also discussed.     

The lowest states of the O3+ ion

A CAS SCF calculation of the potential surfaces for the lowest states of the O₃⁺ ion is reported. An assignment of the bands in the HeI photoelectron spectrum is based upon calculated vibration profiles. This assignment shows the ground state of the ion to have ²B₂ symmetry. Also the weak bands at 15.6, 16.5 and 17.5 eV are reassigned.     

Gas phase high temperature photoelectron spectroscopy: The tin monoxide molecule

The HeI photoelectron spectrum of SnO (X¹Σ⁺) has been recorded. Two bands have been observed corresponding to ionization from the 6π and 13 ionization energies of 9.98 and 10.12 eV respectively. Vibrational structure associated with the first band has been analysed to give

and D_e = 3.23 ± 0.10 eV in the SnO⁺ (X²Π) state. An assessment has been made of the ability of Hartree-Fock-Slater calculations, multiple-scattering SCF-Xα calculations and ab ini energies for the group IV diatomic monoxide molecules.     

Vacuum ultraviolet photoelectron spectroscopy of transient species. XVII. The SiH3(X 2A1) radical

The first band in the vacuum ultraviolet photoelectron spectrum of the silyl radical, corresponding to the process SiH₃ (X ¹A′₁) ← SiH₃(X ²A₁), has been observed with HeI radiation. Extensive vibrational fine structure associated with the SiH₃⁺ deformation vibration was observed in this band and analysis of the structure gave a value of ω = 820 = 40 cm^-1 for the out-of-plane deformation mode in the ion. The vertical and adiabatic ionization energies were measured as 8.74 = 0.01 eV and 8.14 ± 0.01 eV respectively and use of the latter value together with the established heat of formation of the silyl radical allows an improved heat of formation of SiH₃^-. ΔH₂₉₈⁰ (SiH₃^-) to be derived as 980 ± 7 kJ mol^?1.     

Tris (methylidene)-cyclopropane (“[3]Radialene”). Part 2. Electronic states of the molecular cation and revised UV.-absorption spectrum of the parent neutral

The photoelectron spectrum of tris (methylidene)-cyclopropane 1 (“[3]radialene”) is reported and the electronic states of 1 ⁺ assigned. Jahn-teller activity in the degenerate states of 1 ⁺is discussed. Differences in the Franck-Condon profile of the first PE band and the Rydberg series in the Vacuum-UV./UV. absorption spectrum indicate for the Rydberg series (n=3) a ¹A″₂-species, which supports earlier tentative proposals. The high intensity absorption in the 5.5 eV-6 eV energy range of the latter spectrum recorded earlier are definitely due to impurities. The vibrational fine structure of a weak band system around 5.5 eV in our spectrum suggests for this transition S₀→S₂(¹A′₁), which is dipole forbidden but borrows intensity from S₁(¹E′) trough vibronic coupling via an e′-mode. From vapor pressure measurements ε(λ_max=289 nm) = 9390± 1170 for gaseous 1 was found.     

The threshold photoelectron spectrum of silane

The threshold photoelectron spectrum of SiH₄, has been recorded between 11 and 20 eV. The vibrational structure observed in the first band of the HeI PES could not be detected. Between 15 and 18 eV. autoionizing Rydberg states converging to the ²A₁ ionisation limit are observed. They can be interpreted as excitations to npt₂ or ndt₂ orbitals.     

The photoelectron spectrum of HCP and comments on the first photoelectron band of HCN

The photoelectron spectrum of HCP has been obtained, Ionization potentials are found at 10.79 ± 0.01 eV (X² Π) and 12.86 ± 0.01 eV (A ² Σ). By comparison with HCP, a new interpretation of the first photoelectron band of HCN has been proposed which involves a Renner-Teller interaction in the Σ⁺ vibronic states of the molecular ion.     

A study of aluminium monofluoride and aluminium trifluoride by high-temperature photoelectron spectroscopy

The Hel photoelectron spectrum of gaseous AIF(X¹Σ⁺) has been recorded and the first three cationic states have been assigned with the aid of PNO/CEPA calculations. The first band shows vibrational structure and analysis of the component separations and relative intensitives leads to values of ω_c = 1040 ± 40 cm^?1 and r_c = 1.59 ± 0.01 Å in the AIF⁺ (X²Σ⁺) state; the corresponding theoretical values are 960 cm^?1 and 1.60 Å respectively. The first adiabatic ionization potential, 9.73 ± 0.01 eV, allows a determination of the quantum defect, δ, in a number of previously observed Rydberg states of AIF. The Hel photoelectron spectrum of gaseous AIF₃ has also been obtained. It is assigned on the basis of ab initio molecular orbital calculations and comparison with the corresponding BF₃ spectrum.     

Ammonia Borane,NH3BH3: A Threshold Photoelectron–Photoion Coincidence Study of a Potential Hydrogen-Storage Material

We have investigated the photoionization of ammonia borane (AB) and determined adiabatic ionization energy to be 9.26±0.03 eV for the X^{+ 2}E←X ¹A₁ transition. Although the threshold photoelectron spectrum appears at first glance to be similar to the one of the isosteric ethane, the electronic situation differs markedly, due to different orbital energies. In addition, an appearance energy AE_0K(NH₃BH₃, NH₃BH₂⁺)= 10.00±0.03 eV has been determined, corresponding to the loss of a hydrogen atom at the BH₃-site. From the data, a 0 K bond dissociation energy for the B−H bond in the cation of 71.5±3 kJ mol⁻¹ was derived, whereas the one in the neutral compound has been estimated to be 419±10 kJ mol⁻¹.     

Molecular fragmentations: Part I. Structures and energies of molecular fragments derived from formic acid

Molecular geometries and heats of formation are calculated, using MINDO/3, for the following mass-spectral fragment pairs derived from formic acid: X(²A')(HCOOH)⁺; (HCOO)⁺ + H^xxx; (HCO)⁺ + OH; HCO + (OH)⁺; (CO)⁺ + H₂O; (CO₂)⁺ + H₂. The activation energy for the reaction (HCOOH)⁺ → (HCOO)⁺ + H^xxx is 75 kJ mol^?1. A correlation is made of the symmetry classes of the electronic states of (HCOOH)⁺, accessible by single electron excitation, and those of the mass-spectral fragments: it is shown that, despite their closely similar appearance potentials, the ions (HCOO)⁺ and (HCO)⁺ arise from different states of (HCOOH)⁺. The structure of (HCOOH)²⁺ is also reported.     

Ultraviolet photoelectron spectroscopy of the hydrogen bonded heterodimer H2S⋯HCl

The HeI photoelectron spectrum of the hydrogen bonded hetero-dimer H₂S⋯HCl shows two vertical ionization energies at 10.91 and 12.16 eV. Ab initio MO calculations reveal that these features are due to the sulphur and chlorine lone pair ionizations respectively. Results show that while the ground ionic state is repulsive the first excited ionic state is strongly bound. The photoelectron spectrum of the diethyl sulphide⋯HCl complex is similar to that of H₂S⋯HCl     

Vibrational structure in the photoelectron spectrum of O2+2Σg− (σg2s)

Discrete vibrational structure has been observed in the photoelectron spectrum of oxygen at an ionization potential of 40.33 eV. Two levels, attributed to the O₂⁺²Σ_g^?(σ_g2s) final state, have been detected with a vibrational spacing of 0.071 eV.     

FC(O)SNCO的电子结构和光电离解离过程

由于拥有―C(O)S―和―NCO基团, FC(O)SNCO的分子和电子结构是非常有趣的. 利用FC(O)SCl和AgNCO制备了FC(O)SNCO,并利用HeI光电子能谱(PES)、光电离质谱(PIMS)以及理论计算研究了其分子和电子结构. 通过将实验、理论计算以及自然键轨道(NBO)分析结合起来, 获得了FC(O)SNCO的最稳定分子构型. 利用外壳层格林函数(OVGF)方法以及与相似化合物的比较, 对其光电子能谱进行了指认. 理论计算表明,对于中性分子最稳定的构型为syn-syn非平面构型, 而电离后的离子最稳定构型为syn-syn平面构型. 实验结果表明, 第一电离能来自于S的孤对电子轨道, 为10.33 eV. 第二至第六电离能分别为12.03、13.23、13.77、14.78、15.99 eV, 并对这些电离能进行了指认. 在光电离质谱中产生了六个质谱峰, 分别为SN⁺、FC(O)⁺、SNCO⁺、FC(O)SN⁺、C(O)SNCO⁺、FC(O)SNCO^+·, 其中FC(O)SNCO^+·的峰是最强峰. 结合HeI光电子能谱和理论计算, 对PIMS进行了分析,并研究了可能的电离和解离过程并对其进行了讨论.     

High-resolution UV photoelectron spectrum of CO2

The highly-resolved HeI photoelectron spectrum of CO₂ is presented and its vibrational structure studied in detail. In the X? ²Π_g ionic state the v₃ antisymmetric mode is found to be excited in double quanta (v_1-v_2-v₃ = 0. 0. 2) with energy hv₃ = 181 meV. In the C? ²Σ_g⁺ state a single quantum of the same mode is found to be excited (hv₃ = 189 meV) in combination with a v₁ excitation. Vibronic interaction with vibrational levels in the B? ²Σ_u⁺ state of the ion is suggested to promote this (1, 0, 1) excitation. It is established that inelastic scattering processes contribute to the vibrational structure in the C? ²Σ_g⁺ band. The spin-orbit splitting in the X? ²Π_g is determined to be 19±1 meV and 10±2 eV in the ā²Π_u state. Vibronic structure is resolved in the X? ²Π_g band where the Renner-Teller coupling constant is determined to be ? = 0.21±0.02 and the vibrational energy of the v₂ mode as 60±7 meV. In the ā²Π_u state the v₂ energy is found to be hv₂ = 60 meV from the observed hot-band structure.     

The first ionization energy of NO2. What answer can be brought at present by photoelectron spectroscopy?

Reinvestigation of the Ar 1048-1067 Å photoelectron spectrum of NO₂ using a completely NO-free sample suggests an upper limit for the adiabatic first ionization energy of this molecule consistent with the 9.75 eV photoionization value. The very low cross section process observed below 10.0 eV is interpreted by a mechanism involving autoionization followed by radiationless transition toward NO₂⁺ ionic ground state.     

Assignment of the first photoelectron band of the CH<Subscript>3</Subscript>CHCl radical using ab initio quantum mechanical calculations

HeI photoelectron spectra have been recorded for the reaction of atomic fluorine with ethyl chloride at different reaction times. A structured band associated with a short-lived primary reaction product has been recorded with adiabatic and vertical ionization energies of (7.84±0.02) and (8.18±0.02) eV respectively. An average vibrational separation of (680±30) cm^–1was observed in this band. Comparison between the experimental vertical and adiabatic ionization energies and ionization energies computed for CH₃CHCl (X²A) and CH₂CH₂Cl (X²A) at different levels of theory led to the assignment of the observed first photoelectron band to the ionization of CH₃CHCl (X²A). The observed vibrational structure was assigned to excitation of the C–Cl stretching mode in CH₃CHCl⁺(X¹A).Proceedings of the 11th International Congress of Quantum Chemistry satellite meeting in honor of Jean-Louis Rivail     

Oxidation of formic acid by bromine in aqueous,strongly acid media

Spectrophotometric methods were used to investigate the rate of the reaction of Br₂ with HCOOH in aqueous, acidic media. The reaction products are Br^? and CO₂. The kinetics of this reaction are complicated by both the formation of Br₃^? as Br^? is formed and the dissociation of HCOOH into HCOO^? and H⁺. Previous work on this reaction was carried out at acidities lower than the highest used here and led to the conclusion that only HCOO^? reacts with Br₂. It is agreed that this is by far the principal reaction. However, at the highest acidity experiments, an added small component of reaction was found, and it is suggested that it results from the direct reaction of Br₂ with HCOOH itself. On this assumption, values of the rate constants for both reactions are derived here. The rate constant for the reaction of HCOO^? with Br₂ agrees with values previously reported, within a factor of 2 on the low side. The reaction involving HCOOH is more than 2000 times slower than the reaction involving HCOO^?, but it does contribute to the overall rate as [H⁺] approaches 1M. These derived rate constants are able to simulate quantitatively the authors' absorbance-versus-time data, demonstrating the validity of their data treatment methods, if not mechanistic assignments. Finally, activation parameters were determined for both rate constants. The values obtained are: ΔE^?(HCOOH + Br₂) = 13.3 ± 1.1 kcal/mol, ΔS^? (HCOOH + Br₂) = ?28 ± 3 cal/deg mol, ΔE^? (HCOO^? + Br₂) = 13.1 ± 0.9 kcal/mol, and ΔS^?(HCOO^? + Br₂) = ?12 ± 1 cal/deg mol. That the activation energies of the two reactions turn out to be essentially identical does not support the authors' suggestion that both HCOOH and HCOO^? react with Br₂.     

Photoelectron spectrum of hypofluorous acid,HOF

The photoelectron spectrum of HOF has been obtained with He I resonance radiation. Three bands were observed, which can be interpreted by analogy to the diatomic halogens, and to the recently reported CIF. The first two bands can be identified with the out-of-plane and in-plane components of the π_g-like outermost orbital of the diatomic halogens, split by the C_s symmetry of HOF. The first ionization potential is found to be 12.69 ± 0.03 eV, in close agreement with the photoionization value 12.71 ± 0.01 eV.     

HeI photoelectron spectroscopic study of the electronic structure of SSF2 and FSSF compounds

HeI photoelectron (PE) spectra are re-recorded for SSF₂ and FSSF. The assignment of bands has been made with the aid of band shapes, band intensities and ab initio calculations. In the PE spectrum of SSF₂, two sharp peaks at 10.48 and 11.22 eV are considered to result from through-space interaction of lone-pair orbitals in the two S atoms and two sharp peaks at 12.50 and 12.90 eV from through-space interaction of lone-pair orbitals in the two F atoms. The larger splitting of the S atoms can be attributed to the larger 3p orbital of S. The lack of sharp peaks in the PE spectrum of FSSF shows that there is no orbital which embodies the character of a lone-pair. So the PE spectra of SSF₂ and FSSF are examples embodying through-space interaction of lone-pair orbitals.     

The vacuum ultraviolet photoelectron spectrum of difluoramine

The HeI photoelectron spectrum of difluoramine is reported. The seven ionization potentials within the Hel region have been assigned. Extensive vibrational structure on the first band of both HNF₂ and DNF₂, and ab initio calculations of the ionic geometry, indicate that the ground ionic state is planar.