Browsing by Author "Bahou, M"

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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.
Isomers of GeNO and Ge(NO)(2): Production and infrared absorption of GeNO and ONGeNO in solid Ar
(2005-08-01)
Chou, JB
;
Bahou, M
;
Lee, YP
;
Rayner, D
;
Simard, B
Crystalline germanium was ablated with light at 532 nm from a frequency-doubled neodymium: yttrium aluminum garnet laser, and the resultant plume reacted with NO before deposition onto a substrate at 13 K. Lines in group A at 1543.8 and 3059.7 cm(-1) that become enhanced at the initial stage of irradiation at 308 or 193 nm and also after annealing are attributed to nu(1) and 2 nu(1) of GeNO. Lines in group B at 1645.5 and 1482.8 cm(-1) that become diminished after further irradiation of the matrix at 308 or 193 nm but become enhanced after annealing are attributed to symmetric NO stretch (nu(1)) and antisymmetric NO stretch (nu(7)) of ONGeNO. The assignments were derived based on wave numbers and isotopic ratios observed in the experiments with N-15- and O-18-isotopic substitutions and predicted with quantum-chemical calculations. Quantum-chemical calculations with density-functional theories (B3LYP and BLYP/aug-cc-pVTZ) predict four stable isomers of GeNO, six isomers of Ge2NO, and four isomers of Ge(NO)(2), with linear GeNO, cyc-GeNGeO, and cyc-GeONNO having the least energies, respectively. The formation mechanisms of GeNO and ONGeNO are discussed. In addition, a weak line at 1417.0 cm(-1) and two additional lines associated with minor matrix sites at 1423.0 and 1420.3 cm(-1) are assigned to GeNO-. (C) 2005 American Institute of Physics.
Photodissociation dynamics of vinyl chloride investigated with a pulsed slit-jet and time-resolved Fourier-transform spectroscopy
(2004)
Bahou, M
;
Lee, YP
;
應用化學系
;
Department of Applied Chemistry
Following photodissociation of vinyl chloride seeded in a He supersonic jet at 193 nm, rotationally resolved infrared emission of HCl ( v) are recorded to yield nascent rotational and vibrational distributions. Preliminary results show that the rotational distribution of HCl free from rotational quenching deviates slightly from Boltzmann-type distribution and agrees well with trajectory calculations; a portion of the low-J component observed previously in a flow system is attributed to quenching. The implications for photodissociation dynamics are discussed.