Abed Ridha

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

Abstract The first band in the vacuum ultraviolet photoelectron spectrum of the silyl radical, corresponding to the process SiH 3 (X 1 A′ 1 ) ← SiH 3 (X 2 A 1 ), has been observed with HeI radiation. Extensive vibrational fine structure associated with the SiH 3 + 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 SiH 3 - . Δ H 298 0 (SiH 3 - ) to be derived as 980 ± 7 kJ mol −1 .

Gas phase high temperature photoelectron spectroscopy: The tin monoxide molecule

Abstract 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 De = 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.

Study of the ground state of PO+ using photoelectron spectroscopy

The band associated with the first ionization potential of the PO(X2Π) radical, corresponding to the process PO+(X1Σ+)â†� PO(X2Π), has been observed for the first time by vacuum ultraviolet photoelectron spectroscopy. The adiabatic first ionization potential was measured as 8.39 ± 0.01 eV and the following spectroscopic parameters were determined for the PO+(X1Σ+) state: text-decoration:overlinewe= 1410 ± 30 cm–1, re= 1.419 ± 0.005 A, and De= 8.25 ± 0.01 eV.

The first band in the He(I) photoelectron spectrum of the CH2Cl free radical

Abstract The fluorine atom reaction with CH 3 Cl provides the CH 2 Cl free radical for observation of a structured photoelectron band at 8.88 ± 0.01 eV vertical ionization energy with 1020 ± 40 cm −1 vibrational intervals. This spacing is appropriate for the CCl fundamental in CH 2 Cl + based on increase (pp) π bonding in the cation as compared to the free radical.

HeI photoelectron spectra of PH2 and PF2: comparison between simulation and experiment

Molecular orbital calculations on PH2 and PF2 and some of their low-lying cationic states, followed by Franck-Condon calculations, have been performed with the objective of simulating HeI photoelectron band of these radicals. The molecular orbital calculations involved MP2 and CCSD(T) geometry optimization and frequency calculations, with basis sets of size up to 6-311G(3df,2p), and as well as G1/G2 calculations. Franck-Condon simulations of photoelectron bands were performed using force constants derived from the ab initio calculations. Based on comparison between simulated and observed spectra, the first adiabatic ionization energy of PH2 has been confirmed as (9.84 ± 0.01) eV and the lowest singlet-triplet separation in PH2+ (1A1 − 3B1 has been deduced as (0.78 ± 0.04) eV. Also, the first adiabatic ionization energy of PF2, corresponding to the ionization PF2+ 1A2 ← PF2 X2B1, has been established as (8.84 ± 0.01) eV. The vibrational structure observed in the first band of PF2 has been assigned to excitation of the symmetric stretching mode (v1) in PH2 in PF2+(X1A1) and the vibrational structure observed in the second band of PH2 has been assigned to excitation of the deformation mode (v2) in PH2+(a3B1).

A study of the ground electronic states of the isoelectronic ions PF+ and NCI+ by vacuum ultraviolet photoelectron spectroscopy

NCI(a1Δ), prepared from the CI + N3 reaction, and PF(X3Σ–), prepared as a secondary product of the F + PH3 reaction, have been investigated with vacuum ultraviolet photoelectron spectroscopy. The adiabatic ionization energy for the process NCI+(X2Π)â†� NCI(a1Δ) was measured as 9.69 ± 0.02 eV and this has led to a determination of the first adiabatic ionization energy of NCI(X3Σ–) of 10.84 ± 0.02 eV. The first adiabatic ionization energy of PF(X3Σ–) was measured as 9.60 ± 0.01 eV. Spectroscopic constants, e and re, in the ground 2Π state of the ions were determined as 1160 ± 30 cm–1 and 1.489 ± 0.005 A for NCI+ and 1030 ± 30 cm–1 and 1.498 ± 0.005 A for PF+, respectively. Assignments of the observed photoelectron bands have been supported by ab initio SCF-CI molecular-orbital calculations.