Browsing by Author "Sankaran, K"

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Experimental and quantum-chemical studies on photoionization and dissociative photoionization of CH2Br2
(2004-02-15)
Chiang, SY
;
Fang, YS
;
Sankaran, K
;
Lee, YP
;
應用化學系
The dissociative photoionization of CH2Br2 in a region similar to10-24 eV was investigated with photoionization mass spectroscopy using a synchrotron radiation source. An adiabatic ionization energy of 10.25 eV determined for CH2Br2 agrees satisfactorily with predictions of 10.26 and 10.25 eV with G2 and G3 methods, respectively. Observed major fragment ions CH2Br+, CHBr+, and CBr+ show appearance energies at 11.22, 12.59, and 15.42 eV, respectively; minor fragment ions CHBr2+, Br+, and CH2+ appear at 12.64, 15.31, and 16.80 eV, respectively. Energies for formation of observed fragment ions and their neutral counterparts upon ionization of CH2Br2 are computed with G2 and G3 methods. Dissociative photoionization channels associated with six observed fragment ions are proposed based on comparison of determined appearance energies and predicted energies. An upper limit of DeltaH(f,298)(0)(CHBr+)less than or equal to300.7+/-1.5 kcal mol(-1) is derived experimentally; the adiabatic ionization energy of CHBr is thus derived to be less than or equal to9.17+/-0.23 eV. Literature values for DeltaH(f,298)(0)(CBr+)=362.5 kcal mol(-1) and ionization energy of 10.43 eV for CBr are revised to be less than 332 kcal mol(-1) and 9.11 eV, respectively. Also based on a new experimental ionization energy, DeltaH(f,298)(0)(CH2Br2+) is revised to be 236.4+/-1.5 kcal mol(-1). (C) 2004 American Institute of Physics.
Experiments and calculations on photoionization and dissociative photoionization of CH2CO
(2004-08-01)
Chiang, SY
;
Fang, YS
;
Bahou, M
;
Sankaran, K
;
應用化學系
The dissociative photoionization of molecular-beam cooled CH2CO in a region of similar to10-20 eV was investigated with photoionization mass spectrometry using a synchrotron radiation as the light source. Photoionization efficiency curves of CH2CO+ and of observed fragment ions CH2+, CHCO+, HCO+ C2O+ CO+, and C2H2+ were measured to determine their appearance energies. Relative branching ratios as a function of photon energy were determined. Energies for formation of these observed fragment ions and their neutral counterparts upon ionization of CH2CO are computed with the Gaussian-3 method. Dissociative photoionization channels associated with six observed fragment ions are proposed based on comparison of determined appearance energies and predicted energies. The principal dissociative processes are direct breaking of C=C and C-H bonds to form CH2+ + CO and CHCO+ + H, respectively; at greater energies, dissociation involving H migration takes place.