TY - JOUR
T1 - DETERMINATION OF THE FIRST DISSOCIATIVE
IONISATION ENERGY OF POLYATOMIC MOLECULES
BY THRESHOLD PHOTOELECTRON PHOTOION
COINCIDENCE (TPEPICO) SPECTROSCOPY:
T2 - APPLICATION TO CF4, SF6, SeF6, TeF6 AND SF5CF3
AU - Chim, R. Y. L.
AU - Kennedy, R. A.
AU - Tuckett, R. P.
AU - Zhou, Weidong
AU - Jarvis, G. K.
AU - Mayhew, C. A.
AU - Collins, D. J.
AU - Hatherly, P. A.
PY - 2002/2/1
Y1 - 2002/2/1
N2 - A recent paper (Science 2000, 289, 611) has suggested that an anthropogenic greenhouse gas, SF5CF3,
recently detected in the atmosphere, has the highest radiative forcing of any gas-phase molecule. The
ground state of SF5CF+
3 is repulsive in the Franck–Condon region, the parent ion is not observed,
and the onset of ionisation can only give an upper limit to the energy of the first dissociative ionisation
pathway of SF5CF3 (to CF+
3 + SF5 + e−). Using a variation of threshold photoelectron
photoion spectroscopy, we have determined the kinetic energy released into the two fragments over
a range of energies. Using an impulsive model, the data has been extrapolated to zero kinetic energy
to obtain a value for the first dissociative ionisation energy for SF5CF3 of 12.9 ± 0.4 eV. The
enthalpy of formation at 0 K of SF5CF3 is determined to be −1770 ± 47 kJ mol−1, and the dissociation
energy of the SF5–CF3 bond at 0 K to be 392 ± 48 kJ mol−1 or 4.06 ± 0.45 eV. The
implication of this bond strength is that SF5CF3 is very unlikely to be broken down by UV radiation
in the stratosphere. A similar experiment for CF4 (to CF+
3 +F+e−), SF6 (to SF+
5 +
F+e−), SeF6 (to SeF+
5 +F+e−) and TeF6 (to TeF+
5 +F+e−) yielded values for their dissociative
ionisation energies of 14.45 ± 0.20, 13.6 ± 0.1, 14.1 ± 0.5 and 14.5 ± 0.6 eV, respectively.
The first two results agree with previous data on the CF3 and SF5 free radicals. The final two results
yield 0 K enthalpies of formation of SeF+
5 and TeF+
5 to be 166 ± 52 and 4 ± 62 kJ mol−1,
respectively.
AB - A recent paper (Science 2000, 289, 611) has suggested that an anthropogenic greenhouse gas, SF5CF3,
recently detected in the atmosphere, has the highest radiative forcing of any gas-phase molecule. The
ground state of SF5CF+
3 is repulsive in the Franck–Condon region, the parent ion is not observed,
and the onset of ionisation can only give an upper limit to the energy of the first dissociative ionisation
pathway of SF5CF3 (to CF+
3 + SF5 + e−). Using a variation of threshold photoelectron
photoion spectroscopy, we have determined the kinetic energy released into the two fragments over
a range of energies. Using an impulsive model, the data has been extrapolated to zero kinetic energy
to obtain a value for the first dissociative ionisation energy for SF5CF3 of 12.9 ± 0.4 eV. The
enthalpy of formation at 0 K of SF5CF3 is determined to be −1770 ± 47 kJ mol−1, and the dissociation
energy of the SF5–CF3 bond at 0 K to be 392 ± 48 kJ mol−1 or 4.06 ± 0.45 eV. The
implication of this bond strength is that SF5CF3 is very unlikely to be broken down by UV radiation
in the stratosphere. A similar experiment for CF4 (to CF+
3 +F+e−), SF6 (to SF+
5 +
F+e−), SeF6 (to SeF+
5 +F+e−) and TeF6 (to TeF+
5 +F+e−) yielded values for their dissociative
ionisation energies of 14.45 ± 0.20, 13.6 ± 0.1, 14.1 ± 0.5 and 14.5 ± 0.6 eV, respectively.
The first two results agree with previous data on the CF3 and SF5 free radicals. The final two results
yield 0 K enthalpies of formation of SeF+
5 and TeF+
5 to be 166 ± 52 and 4 ± 62 kJ mol−1,
respectively.
U2 - 10.1142/S0218625X02002087
DO - 10.1142/S0218625X02002087
M3 - Article
SN - 0218-625X
VL - 09
SP - 129
EP - 135
JO - Surface Review and Letters
JF - Surface Review and Letters
IS - 01
ER -