Neutralized ionbeam studies of the rare gas hydrides: Observation of unique metastability for NeH J. Chem. Phys. 88, 3116 (1988); 10.1063/1.453955 Observation and characterization of the CH5 radical by neutralized ion beam techniques J. Chem. Phys. 87, 5804 (1987); 10.1063/1.453504 The n=2,3 triplet Rydberg states of the HD molecule observed by fast neutralbeam photofragment spectroscopy J. Chem. Phys. 86, 3050 (1987); 10.1063/1.452010 Experimental observations of excited dissociative and metastable states of H3 in neutralized ion beamsThe N 2 H(D) radical has been studied experimentally by measurement ofthe kinetic energy release in its unimolecular dissociation following formation by electron transfer from metal atoms to high velocity, mass-resolved ion beams and theoretically by ab initio techniques. Calculations ofthe dissociation coordinate of the ground state radical at the MP4/6-311G*"'1 I MP3/6-311G*'" level of theory indicate that the radical is unstable with respect to N2 and H by 0.6 eV but separated from the dissociation products by a 0.4 eV Qarrier. One dimensional tunneling lifetimes are determined to be 7.0X 10-12 s for N2H and 3.6X 10-10 s for N2D.Neutralization of the ion by Zn targets produces predominantly radicals in the 2A I ground state with dissociative lifetimes 1" < 0.5 its, in agreement with the calculations. Mg targets produce the radical in a mixture of the 2 A I ground and 2 A "( 'IT) excited states with a branching ratio dependent on the internal energy of the precursor ion. A higher excited state of the radical, suggested to be an n = 3 Rydberg level, is produced with K targets and is inferred to undergo radiative transitions, probably containing some discrete structure, to the lower 2A I and 2A " ( 'IT) states in the wavelength range of 2700-4500 A. Observations of these transitions may constitute the first spectroscopic observation of the radical.
The rare gas hydride radicals have been produced by charge exchange of the corresponding ion in a mass selected, high velocity beam with K, Na, Mg, Zn, or Hg target metals. NeH shows unique behavior, being produced in both dissociative and long-lived (>5.0 μs) metastable states. Arguments based on energetic considerations are presented that the observed metastability should be associated with the ground state of the NeH radical, requiring that it have a shallow well and dissociation barrier analogous to those previously determined for the ground states of the isoelectronic NH4, H3O, and H2F radicals. The existence of a structured radiative transition near 6.1 eV is predicted for the NeH radical. The other rare gas hydrides exhibit only dissociation of the radical with the kinetic energy released explainable in terms of production of known electronic states of the radicals by near resonant electron transfer. For HeH and ArH the first excited electronic state (A 2Σ+) is observed to efficiently predissociate into the repulsive ground state, whereas for KrH and XeH, lower limits of 4.5 and 3.9 eV, respectively, are determined for the energies of the corresponding excited states with respect to the separated ground state atoms.
Articles you may be interested inMass spectrometric detection of neutral radicals in a CH4 microwave discharge by use of Li+ ion attachment techniques Stability of the ammonium and methylammonium radicals from neutralized ionbeam spectroscopy The CHs (CDs) radical has been produced by charge transfer neutralization of fast ion beams using Na and Zn targets. The results obtained with Na targets are in excellent agreement with previous similar studies using alkali metal targets. In particular, no evidence for metastability was observed. Alternatively, results obtained with Zn targets show clear evidence for production of metastable states of the radical with lifetimes in the 1-10 /1-s range. Measurement of the kinetic energy released upon dissociation indicates that some neutral radicals produced in CHl (CDs+ )/Zn reactions have energies very close to the ionization limit. It is proposed that the observed metastability may be explained by the production of high Rydberg levels of the radical having sufficiently long radiative lifetimes.5804
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