TY - JOUR
T1 - Fragmentation pathways in the dissociation of fluoro-iodo-benzene negative ions
AU - Lobo, R. F. M.
AU - Moutinho, A. M. C.
AU - Calhorda, M. J.
N1 - Prof. J. Los from FOM Institute in Amsterdam is gratefully acknowledged for his important contribution in the analysis of this work. The authors also wish to thank the support from Fundacão para a Ciência e Tecnologia for the work at the Centro de Física Molecular da Universidade Técnica de Lisboa and at the Physics Department of Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa.
PY - 1998/8/15
Y1 - 1998/8/15
N2 - In a crossed-beam configuration between a fast potassium atom beam (10-350 eV) and a thermal beam of fluoro-iodo-benzene molecules, the total yields of parent and fragment negative ions have been measured. The measurements include all three isomers: ortho-, para- and meta-fluoro-iodo-benzene. The negative ions are extracted from the interaction region by a pulsed extraction voltage. Mass selection is obtained by applying a time-of-flight (TOF) method. Apart from the parent ion C6H4IF- (m=222) the fragment ions C6H4F- (m=95), C4H3F- (m=70), C3H2F- (m=57) and C2HF- (m=44) are formed in the electron transfer collision. From the TOF spectra it is concluded that the fragmentation of energy-rich ions, for the three isomers, follows two paths. Either the I-atom is expelled, leaving the ring intact, or the ring is opened followed in a second step by further fragmentation. Calculations are performed applying the extended Hückel method to establish the orbitals in which the electron is captured. Evidence is presented that the LUMO and the second LUMO for all three isomers are only separated by a few tenths of an electron volt. Both orbitals are strongly antibonding π* ring orbitals.
AB - In a crossed-beam configuration between a fast potassium atom beam (10-350 eV) and a thermal beam of fluoro-iodo-benzene molecules, the total yields of parent and fragment negative ions have been measured. The measurements include all three isomers: ortho-, para- and meta-fluoro-iodo-benzene. The negative ions are extracted from the interaction region by a pulsed extraction voltage. Mass selection is obtained by applying a time-of-flight (TOF) method. Apart from the parent ion C6H4IF- (m=222) the fragment ions C6H4F- (m=95), C4H3F- (m=70), C3H2F- (m=57) and C2HF- (m=44) are formed in the electron transfer collision. From the TOF spectra it is concluded that the fragmentation of energy-rich ions, for the three isomers, follows two paths. Either the I-atom is expelled, leaving the ring intact, or the ring is opened followed in a second step by further fragmentation. Calculations are performed applying the extended Hückel method to establish the orbitals in which the electron is captured. Evidence is presented that the LUMO and the second LUMO for all three isomers are only separated by a few tenths of an electron volt. Both orbitals are strongly antibonding π* ring orbitals.
UR - http://www.scopus.com/inward/record.url?scp=0032372075&partnerID=8YFLogxK
U2 - 10.1016/S0301-0104(98)00152-9
DO - 10.1016/S0301-0104(98)00152-9
M3 - Article
AN - SCOPUS:0032372075
SN - 0301-0104
VL - 234
SP - 265
EP - 275
JO - Chemical Physics
JF - Chemical Physics
IS - 1-3
ER -