Photoionization and ion cyclotron resonance studies of the reaction C/sub 2/H/sub 4//sup +/ + C/sub 2/H/sub 4/. -->. C/sub 3/H/sub 5//sup +/ + CH/sub 3/

Journal Article · Sat Mar 01 00:00:00 EDT 1975 · J. Chem. Phys.; (United States)

OSTI ID:7204246

LeBreton, P R ^[1]; Williamson, A D; Beauchamp, J L; Huntress, W T

---

1. California Inst. of Tech., Pasadena

High pressure photoionization mass spectrometry has been employed to study the ion molecule reaction C/sub 2/H/sub 4//sup +/ + C/sub 2/H/sub 4/ ..-->.. C/sub 3/H/sub 5//sup +/ + CH/sub 3/ at wavelengths between 700 and 1180 A. Measurements have been made of the apparent ionization cross section of both C/sub 2/H/sub 4//sup +/ and C/sub 3/H/sub 5//sup +/ as a function of photon energy. The threshold energy for the reaction is 10.51 eV. The reaction cross section decreases as the internal energy of the ionic reactant increases. Vibrational structure, observed in the C/sub 2/H/sub 4//sup +/ photoionization efficiency curve immediately above threshold (10.51--11.7 eV) permits a rough estimate of the change in reaction cross section with vibrational excitation. In the energy region between 11.7 and 12.1 eV a slight increase in the C/sub 2/H/sub 4//sup +/ photoionization efficiency curve appears which is not reflected in the C/sub 3/H/sub 5//sup +/ curve. A large increase in the photoionization efficiency curve of C/sub 2/H/sub 4/+ occurs at 12.2 eV, the threshold of the /sup 2/B/sub 3/ first excited electronic state of the ion. A dramatic decrease is observed in the reaction probability of C/sub 2/H/sub 4//sup +/ formed at energies above 12.2 eV. The cross section for reaction in the excited /sup 2/B/sub 3/ state is equal to or less than 13% of the cross section for reaction in the lowest vibrational level of the ground electronic state. The observed decrease in reactivity is independent of repeller voltage at ion exit energies below 3 eV. Pressure studies reveal that after one or two collisions, the reactivity of C/sub 2/H/sub 4//sup +/ is re-established, suggesting that relaxation of internal excitation is an efficient process. The change in reactivity of C/sub 2/H/sub 4//sup +/ with internal energy is compared to the effects of tranlation excitation as determined using the techniques of ion cyclotron resonance spectroscopy. (auth)

• OSTI ID: 7204246
• Journal Information: J. Chem. Phys.; (United States), Vol. 62:5
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
ETHYLENE
ION-MOLECULE COLLISIONS
CATIONS
CHEMICAL REACTIONS
CROSS SECTIONS
IONIZATION
MASS SPECTROSCOPY
PHOTOIONIZATION
VIBRATIONAL STATES
ALKENES
CHARGED PARTICLES
COLLISIONS
ENERGY LEVELS
EXCITED STATES
HYDROCARBONS
ION COLLISIONS
IONS
MOLECULE COLLISIONS
ORGANIC COMPOUNDS
SPECTROSCOPY
640304* - Atomic
Molecular & Chemical Physics- Collision Phenomena