Molecular-beam photoionization studies of molecules and their van der Waals clusters
A new photoionization apparatus incorporating a supersonic molecular beam, a quadrupole mass spectrometer and a 3-meter vacuum ultraviolet monochromator has been used to study the nitric oxide, carbon disulfide, carbonyl sulfide and acetylene molecules along with their van der Waals clusters. Using a wavelength resolution of 0.14 A (FWHM), photoionization efficiency curves were obtained for NO, CS/sub 2/, OCS, and C/sub 2/H/sub 2/ in the respective threshold regions and ionization energy determinations accurate to within 3 MeV were made. The autoionization structures resolved have led to new interpretations and assignments to Rydberg levels. Photoionization efficiency data for the clusters were obtained under lower resolution, typically 1.4 A (FWHM) and led to binding energy determinations of the cluster ions. Other thermochemical values were deduced from fragment appearance energies and sharp rises in ionization efficiencies. From the (CS/sub 2/)/sub 2/ fragment curves, relative reaction probabilities for the formation of the various product channels as a function of the Rydberg level n were determined for CS/sub 2/*(V,n) CS/sub 2/ and the branching ratios were measured for the reaction CS/sub 2/*(V,n) + CS/sub 2/. The shifts observed in the autoionization peaks of the triatomic molecules CS/sub 2/ and OCS due to clustering was investigated and a model is proposed which accounts for these characteristics. Ionization of the acetylene dimer and trimer resulted in clusters which could rearrange to form ions of a more stable configuration. Energy dependence measurements of the acetylene dimer fragmentation process yielding C/sub 4/H/sub 3//sup +/ and C/sub 4/H/sub 2//sup +/ were found to be consistent with predictions based on the quasi-equilibrium theory.
- Research Organization:
- Ames Lab., IA (USA)
- DOE Contract Number:
- W-7405-ENG-82
- OSTI ID:
- 6876579
- Report Number(s):
- IS-T-1009; ON: DE83004967
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400500* -- Photochemistry
640304 -- Atomic
Molecular & Chemical Physics-- Collision Phenomena
74 ATOMIC AND MOLECULAR PHYSICS
ACETYLENE
ALKYNES
AUTOIONIZATION
BEAMS
CARBON COMPOUNDS
CARBON OXYSULFIDE
CARBON SULFIDES
CHALCOGENIDES
DATA
ENERGY LEVELS
EQUATIONS
EXCITED STATES
EXPERIMENTAL DATA
HYDROCARBONS
INFORMATION
IONIZATION
MOLECULAR BEAMS
MOLECULES
NITRIC OXIDE
NITROGEN COMPOUNDS
NITROGEN OXIDES
NUMERICAL DATA
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
RYDBERG EQUATION
SULFIDES
SULFUR COMPOUNDS