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The pulsed field ionization-photoelectron (PFI-PE) spectrum of allyl radical CH2CHCH2 (C3H5) in the energy range of 65 200–66 600 cm-1 has been measured using vacuum ultraviolet laser. Based on the simulation of the rotational structures resolved in the vibrational PFI-PE bands of C3H5+(X 1A1;00+ and ν7+=1), the ionization energies (IEs) of C3H5(X 2A2;00) to form C3H5+(X 1A1;00+ and ν7+=1) are determined to be 65 584.6±2.0 cm-1 (8.131 46±0.000 25 eV) and 66 020.9±2.0 cm-1 (8.185 56±0.000 25 eV), respectively, where ν7+(a1) is the symmetric C–C–C bending mode of C3H5+(X 1A1). These values are compared to IE(C3H5) values obtained in previous experimental and high-level ab initio quantum theoretical studies. [ABSTRACT FROM AUTHOR]

Negative ion photoelectron spectroscopy has been used to study the HCCN[sup -] and HCNC[sup -] ions. The electron affinities (EA) of cyanocarbene have been measured to be EA(HCCN&Xtilde;[sup 3]&Zigma-=2.003 ±0.014eV and EA(DCCN&Xtilde;[sup 3]&Zigma;[sup -])= 2.009± 0.020 eV. Photodetachment of HCCN[sup -] to HCCN&Xtilde;[sup 3]&Zigma;[sup -] shows a 0.4 eV long vibrational progression in υ[sub 5], the H-CCN bending mode; the HCCN[sup -] photoelectron spectra reveal excitations up to 10 quanta in υ[sup 5]. The term energies for the excited singlet state are found to be T[sub 0](HCCN ã[sup 1] A') = 0.515 ± 0.016 eV and T[sub 0](DCCN ã [sup 1]A') = 0.518 ± 0.027 eV. For the isocyanocarbene, the two lowest states switch and HCNC has a singlet ground state and an excited triplet state. The electron affinities are EA(HCNC&Xtilde;[sup 1]A')=l.883 ± 0.013 eV and EA(&Xtilde;[sup 1]A' DCNC)= 1.877 ± 0.010 eV. The term energy for the excited triplet state is T[sub 0](HCNC ã [sup 3]A") = 0.050 ± 0.028 eV and T[sub 0](DCNC ã[sup 3]A") = 0.063 ± 0.030 eV. Proton transfer kinetics in a flowing afterglow apparatus were used to re-measure the enthalpy of deprotonation of CH[sub 3]NC to be Δ[sub acid]H[sub 298](CH[sub 3]NC) = 383.6 ± 0.6 kcal mol[sup -1]. The acidity/EA thermodynamic cycle was used to deduce D[sub 0](H-CHCN) = 104± 2 kcal mol[sup -1] [ Δ[sub f]H[sub 0](HCCN) = 110 ± 4 kcal mol[sup -1]] and D[sub 0](H-CHNC)= 106±4 kcalmo1[sup -1] [Δ[sub f]H[sub 0](HCNC)= 133±5 kcalmol[sup -1]]. [ABSTRACT FROM AUTHOR]

We have measured the negative ion photoelectron spectra of CH2N- and CD2N- and find the electron affinities: EA(CH2N)=0.511±0.008 eV and EA(CD2N)=0.498±0.011 eV. Franck–Condon simulations of these spectra are carried out and we estimate the CH2N- and CH2N geometry differences; we fit our spectra with the following [constrained] molecular structures. We combine our EA(CH2N) with the results of previous gas phase ion studies to extract a number of thermochemical parameters (kcal/mol): Do0(CH2N–H)=85±5, Do0(H–HCN)=23±6, Do0(H2C–N)=144±6, and the isomerization enthalpy of H2CN+→HCNH+ is ΔHisom(C2v→C∞v)=-51±7. Attempts to calculate the geometry and vibrational frequencies of the H2CN radical are disappointing. Unrestricted Hartree–Fock and second-order Mo\ller–Plesset ab initio calculations in a 6-31++G** basis produce badly spin-contaminated wave functions which do not reproduce the experimental findings. [ABSTRACT FROM AUTHOR]

We have studied the photoelectron spectra of BH-3 and BD-3 and have measured the electron affinities of borane; we find EA(BH3)=0.038±0.015 eV and EA(BD3)=0.027±0.014 eV. The peak splittings and intensities demonstrate that the BH-3 ion and the BH3 neutral have very similar geometries; our spectra are consistent with a planar structure for both species. Variational calculations of a coupled oscillator basis over an ab initio potential give an excellent fit to the experimental frequencies and photodetachment Franck–Condon factors. This ab initio model leads to equilibrium geometries with both BH3 and BH-3 as planar molecules with re(BH-3) =1.207 Å and re(BH3)=1.188 Å. We find ΔH○f0(BH-3) =23.1±3.8 kcal mol-1. [ABSTRACT FROM AUTHOR]

We have measured the photoelectron spectrum of Si-2 and find that the molecular electron affinity is EA(Si2)=2.199±0.012 eV. This spectrum apparently involves multiple electronic states of the Si-2 ion as well as several electronic states of the final neutral, Si2. In order to unravel our experimental findings, we have carried out ab initio MCSCF+1+2 CI calculations on both species. These calculations suggest that there are two nearly degenerate states for both Si2 and Si-2. We can fit our experimental data by assuming detachment from two states of Si-2 :X (2Π) [re=2.187 Å] and A (2Σ+g) [T0=0.117±0.016 eV, re=2.127 Å]. We observe two final states of Si2: X (3Σ-g) [re=2.246 Å] and A (3Πu) [T0=0.053±0.015 eV, re=2.171 Å]. These assignments are confirmed by an experimental study of the angular distributions of the photodetached electrons. [ABSTRACT FROM AUTHOR]

The photoelectron spectroscopy of HO-2 and DO-2 has been studied. We find the electron affinities (E.A.) of the corresponding radicals to be E.A.(HO2)=1.078±0.017 eV and E.A.(DO2)=1.089±0.017 eV; the gas phase acidity of hydrogen peroxide is ΔH○acid (HO2–H) =376.4 ±0.6 kcal/mol. The electron spectra show only one active mode which we assign as the HO–O stretch (ω3). By modeling the Franck–Condon factors we deduce a molecular structure for the HO-2 ion: r0(HO–O)=1.50 Å, r0(H–OO)=0.97 Å, and /_ (H–O–O)=104°. A parallel set of GVB/PP, GVB-CI, and POL-CI ab initio electronic structure computations has been carried out for this ion. [ABSTRACT FROM AUTHOR]

Imaging photoelectron photoion coincidence (iPEPICO) spectra of cyclopentadienone (C5H4=O and C5D4=O) have been measured at the Swiss Light Source Synchrotron (Paul Scherrer Institute, Villigen, Switzerland) at the Vacuum Ultraviolet (VUV) Beamline. Complementary to the photoelectron spectra, photoionisation efficiency curves were measured with tunable VUV radiation at the Chemical Dynamics Beamline at the Advanced Light Source Synchrotron (Lawrence Berkeley National Laboratory, Berkeley, CA, USA). For both experiments, molecular beams diluted in argon and helium were generated from the vacuum flash pyrolysis ofo-phenylene sulphite in a resistively heated microtubular SiC flow reactor. The Franck–Condon profiles and ionisation energies were calculated at the CCSD(T) level of theory, and are in excellent agreement with the observed iPEPICO spectra. The ionisation energies of both cyclopentadienone-d0, IE(C5H4=O), and cyclopentadienone-d4,IE(C5D4=O), were observed to be the same: 9.41 ± 0.01 eV. The mass-selected threshold photoelectron spectrum (ms-TPES) of cyclopentadienone reveals that the C=C stretch in the ground state of the cation is excited upon ionisation, supporting computational evidence that the ground state of the cation is2A2, and is in agreement with previous studies. However, the previously reported ionisation potential has been improved considerably in this work. In addition, sinceo-benzoquinone (o-O=C6H4=O ando-O=C6D4=O) is also produced in this process, its ms-TPES has been recorded. From the iPEPICO and photoionisation efficiency spectra, we infer an adiabatic ionisation energy ofIE(o-O=C6H4=O) = 9.3 ± 0.1 eV, but the rather structureless spectrum indicates a strong change in geometry upon ionisation making this value less reliable. [ABSTRACT FROM AUTHOR]

Presents a correction to the article 'Photoelectron Spectroscopy of CH[sub2]N[sup-].'

The pulsed field ionization-photoelectron (PFI-PE) spectrum of allyl radical CH2CHCH2 (C3H5) in the energy range of 65 200–66 600 cm-1 has been measured using vacuum ultraviolet laser. Based on the simulation of the rotational structures resolved in the vibrational PFI-PE bands of C3H5+(X 1A1;00+ and ν7+=1), the ionization energies (IEs) of C3H5(X 2A2;00) to form C3H5+(X 1A1;00+ and ν7+=1) are determined to be 65 584.6±2.0 cm-1 (8.131 46±0.000 25 eV) and 66 020.9±2.0 cm-1 (8.185 56±0.000 25 eV), respectively, where ν7+(a1) is the symmetric C–C–C bending mode of C3H5+(X 1A1). These values are compared to IE(C3H5) values obtained in previous experimental and high-level ab initio quantum theoretical studies. [ABSTRACT FROM AUTHOR]

Examines the measurement of the negative-ion photoelectron spectra of the methyl, methyl-d[sub 3], and ethyl hydroperoxide anions. Heat formation of the peroxyl radicals; Importance of alkyl peroxyl radicals in atmospheric and combustion processes; Role of alkyl peroxides in the chemistry of combustion.

The benzaldehyde radical anion was produced in the gas phase and studied using negative ion photoelectron spectroscopy. Analysis of the photoelectron spectrum found the adiabatic electron affinity, EA a (C 6 H 5 CHO), to be 0.35 ± 0.05 eV. Two active modes of benzaldehyde are observed in the photodetachment of the C 6 H 5 CHO ̄ anion: ν 7 , the C O stretch (1728 cm −1 ) and ν 6 , the non-phenyl C H stretch (2806 cm −1 ). DFT electronic structure calculations have been carried out and are in agreement with the experimental spectrum. The optimized geometries of both C 6 H 5 CHO X ˜ 1 A′ and C 6 H 5 CHO ̄ X ˜ 2 A” are planar. The excess electron in the benzaldehyde anion is found to be delocalized in its π* (a”) anti-bonding orbital. [ABSTRACT FROM AUTHOR]