Photoionization mass spectrometric studies of the transient species Si sub 2 H sub n ( n =2--5)
- Chemistry Division, Argonne National Laboratory, Argonne, Illinois 60439 (USA)
The transient species Si{sub 2}H{sub 5}, Si{sub 2}H{sub 4}, Si{sub 2}H{sub 3}, and Si{sub 2}H{sub 2} have been prepared for the first time, by reactions of F atoms with Si{sub 2}H{sub 6}. The species are generated {ital in} {ital situ} and studied by photoionization mass spectrometry. The adiabatic ionization potentials are (in eV) Si{sub 2}H{sub 5}, 7.60{plus minus}0.05; Si{sub 2}H{sub 4}, 8.09{plus minus}0.03; Si{sub 2}H{sub 3}, {lt}7.59; and Si{sub 2}H{sub 2}, 8.20{sup +0.01}{sub {minus}0.02}. In addition, two fragment appearance potential curves were measured, Si{sub 2}H{sup +}{sub 3} (Si{sub 2}H{sub 5}) and Si{sub 2}H{sup +}{sub 2} (Si{sub 2}H{sub 4}). By combining these ionization potentials with appearance potentials obtained here and from Si{sub 2}H{sub 6}, the following heats of formation (kcal/mol at 0 K) have been inferred: Si{sub 2}H{sub 5}, {lt}63.3 (59.2); Si{sub 2}H{sub 4}, 67.9{plus minus}0.9; Si{sub 2}H{sub 3} ({similar to}96); Si{sub 2}H{sub 2}, {lt}100.7 (90.2--95.6). The quantities in parentheses are probable values, but less well defined. Structures and structural changes resulting from photoionization are discussed. In particular, Si{sub 2}H{sub 2} and its cation are very likely cyclic (doubly bridged). Heats of formation of cations are also obtained, from which the proton affinities of Si{sub 2}H{sub 2} (199{plus minus}3 kcal/mol) and Si{sub 2}H{sub 4} (199.9 kcal/mol) are deduced. The structural and energetic differences between corresponding silicon and carbon hydrides are discussed in detail.
- Research Organization:
- Argonne National Laboratory (ANL), Argonne, IL
- DOE Contract Number:
- W-31109-ENG-38
- OSTI ID:
- 5614769
- Journal Information:
- Journal of Chemical Physics; (United States), Journal Name: Journal of Chemical Physics; (United States) Vol. 95:4; ISSN JCPSA; ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400201* -- Chemical & Physicochemical Properties
ENTHALPY
FORMATION HEAT
HYDRIDES
HYDROGEN COMPOUNDS
IONIZATION
IONIZATION POTENTIAL
MASS SPECTROSCOPY
ORGANIC COMPOUNDS
ORGANIC SILICON COMPOUNDS
PHOTOIONIZATION
PHYSICAL PROPERTIES
REACTION HEAT
SILANES
SILICON COMPOUNDS
SPECTROSCOPY
THERMODYNAMIC PROPERTIES