Multiphoton ionization as a probe of molecular photofragmentation: statistical and dynamical energy partitioning in the multiphoton dissociation of nitromethane
Multiphoton ionization (MPI) appears in its first use as a probe of laser-induced photofragmentation. Specifically, MPI here reveals the internal and translational energy content of the nascent fragments from the infrared multiphoton dissociation (MPD) of nitromethane (CH/sub 3/NO/sub 2/). The apparatus for this work consists of a pulsed supersonic molecular beam crossed by two pulsed and focused lasers - a CO/sub 2/ laser to induce collision-free unimolecular dissociation of CH/sub 3/NO/sub 2/, and a tunable dye laser following immediately to ionize selectively one of the pair of dissociation fragments for detection by a mass spectrometer and particle multiplier. A computer simulation of each fragment's MPI spectrum, a series of four photon resonances to members of the npsigma/sub u/ Rydberg state of NO/sub 2/ and three photon resonances to two vibrational members of the ..gamma../sub 1/ Rydberg state of CH/sub 3/, aids in determining the fragment's internal energy content. The dye laser is delayed and its focus is traced through a small quarter circle centered at the focus of the CO/sub 2/ laser. The flight times of the fragments from the point of dissociation and their laboratory scattering angular distributions at fixed ionizing laser wavelength provide their center of mass recoil velocity distributions. The energy deposited in the fragments evidences a striking mixture of statistical and dynamical energy partitioning. The statistical RRKM theory of unimolecular decomposition accurately predicts the amount of internal energy found in the fragments.
- Research Organization:
- Cornell Univ., Ithaca, NY (USA)
- OSTI ID:
- 6248030
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
Molecular & Chemical Physics-- Atomic & Molecular Properties & Theory
74 ATOMIC AND MOLECULAR PHYSICS
BEAMS
CARBON DIOXIDE LASERS
CHEMICAL EXPLOSIVES
COMPUTERIZED SIMULATION
DECAY
DISSOCIATION
DYE LASERS
ENERGY LEVELS
EXCITED STATES
EXPLOSIVES
GAS LASERS
IONIZATION
LASERS
LIQUID LASERS
MOLECULAR BEAMS
MULTI-PHOTON PROCESSES
NITRO COMPOUNDS
NITROMETHANE
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
RYDBERG STATES
SIMULATION