Stereochemical and angular momentum constraints in the photodissociation of ammonia

Ashfold, Michael N. R.; Dixon, Richard N.; Irving, S. J.; Koeppe, Hm; Meier, W.; Nightingale, Jen; Schnieder, L.; Welge, K. H.

doi:10.1098/rsta.1990.0121

Cited by 27 publications

(10 citation statements)

References 8 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…fragment with a particular internal energy is dependent upon the pH2 vibrational state density at that particular energy) led these authors to enquire whether this photodissociation process should be viewed as an example of a "statistical" fragmentation (42). Such a process would be somewhat surprising given the demonstrable role of dynamics in establishing the product energy disposal in the corresponding photofragmentation of NH3 (28)(29)(30). The present results, particularly the partially resolved structure around the maximum in the total kinetic energy spectrum, suggest that such is not the case.…”

Section: Discussionmentioning

confidence: 99%

“…Photodissociation of NH3 following excitation-at the long wavelength end of its A-x transition yields NH2(X) fragments, primarily in their vibrationless level and in the specific subset of rotational states that have N -K,. The observed propensity for a-axis rotational excitation of the molecular fragment has been rationalised in terms of the Franck-Condon excitation of out-of-plane bending motion in the parent molecule, amplified by thg presence of the deep conical intersection between the A and X states of the parent at planar configurations in the H---NH, exit channel, through which the dissociating molecule must pass in order to yield ground state fragments (28)(29)(30). The physics of pH3 dissociation following excitation to its A I A~ state must show many parallels.…”

Section: Discussionmentioning

confidence: 99%

“…The time-of-flight (TOF) spectra of the H atoms resulting from photodissociation of NH3 following excitation to each of a number of vibronic levels of the A'A; state showed well resolved struture. Analysis of thjs structure revealed a strong propensity for the partner NH2(X) fragments to be formed with little vibrational excitation, but with large amounts of rotational excitation, specifically concentrated about the a-inertial axis (28)(29)(30). Such product rotational energy disposal can be directly correlated to the effects of the conical intersection, in the H2N---H dissociation channel, through which the dissociating NH,(A) molecules must pass in order to reach the H + NH2 asymptote (28)(29)(30)33).…”

Section: Introductionmentioning

confidence: 99%

“…Analysis of thjs structure revealed a strong propensity for the partner NH2(X) fragments to be formed with little vibrational excitation, but with large amounts of rotational excitation, specifically concentrated about the a-inertial axis (28)(29)(30). Such product rotational energy disposal can be directly correlated to the effects of the conical intersection, in the H2N---H dissociation channel, through which the dissociating NH,(A) molecules must pass in order to reach the H + NH2 asymptote (28)(29)(30)33). Finally, given detailed knowledge of the identities and-energies of these high angular momentum states of the NH2(X) products it has since proved possible to assign their LIF excitation spectra and thereby deduce improved bending potential energy functions for both the ground^^^^ and first excited A2AI states of the NH2 radical (34).…”

Section: Introductionmentioning

confidence: 99%

“…Such conclusions were reiterated in a more recent study of the Doppler lineshape of the resulting H atom photofragments (26). However, any quantitative understanding of the energy disposal in this dissociation, and its specific dependence on parent quantum state, had to await the development of the technique of H atom photofragment translational spectroscopy by Welge and co-workers (27)(28)(29)(30)(31)(32). The time-of-flight (TOF) spectra of the H atoms resulting from photodissociation of NH3 following excitation to each of a number of vibronic levels of the A'A; state showed well resolved struture.…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

Near ultraviolet photolysis of phosphine studied by H atom photofragment translational spectroscopy

Lambert¹,

Morley²,

Mordaunt³

et al. 1994

Can. J. Chem.

View full text Add to dashboard Cite

. Can. J. Chem. 72,977 (1 994).We report time-of-flight measurements of the H atom fragments arising in the photodissociation of phosphine at three near ultraviolet excitation wavele_ngths -2 18.2 nm, 221.6 nm, and 228.0 nm. For these wavelengths, energetic considerations dictate that ground state PH2(X) fragments must be the partner product of the primary photolysis event. The measured H atom kinetic energy distributions indicate that internal excitation of these partner fragments accounts for the major part (362%) of the available energy, in excess of that required to break the H-pH2 bond, provided by the photon. Inspection of the poorly resolved structure evident near the peak of the H atom kinetic energy distribution suggests the presence of substantial bending excitation and a-axis rotational excitation in the pH2 partner fragment. The_H atom kinetic energy distribution also shows clear evidence of atoms arising from secondary photolysis of the primary PH,(X) fragments. This second_ary photo-dissociation is observed to show a marked anisotropy, consistent with a perpendicular photo-excitation of the PH2(X) fragment. Arguments are presented which indicate that the secondary photolysis leads both to the formation of PH(X) fragments, carrying high levels of rotational excitation, and to the three-body atomisation process. On a effectuC des mesures en temps de vol des atomes d'hydrogkne, sous la forme de fragments provenant de la photodissociation de la phosphine B trois longueurs d'onde d'excitation -218,2, 221,6 et 2230 nm -proches de l'ultraviolet. Pour ces longueurs d'onde, des considCrations CnergCtiques dictent que les fragments PH2(X) de 1'Ctat fondamental doivent Etre les produits partenaires de la photolyse primaire. Les distributions de l'knergie cinCtique mesurCes pour les atomes d'hydrogbne indiquent que l'excitation interne de ces fragments partenaires tient compte de la plus grande partie (362%) de 1'Cnergie disponible B partir du photon, ce qui est supCrieur B 1'Cnergie requise pour briser la liaison H-pH2. Un examen minutieux de la structure ma1 rCsolue prCsente prks du pic de la distribution de 1'Cnergie cinCtique des atomes d'hydrogkne suggkre la prCsence d'une excitation importante de dkformation et d'une excitation rotationnelle le long de l'axe a du fragment partenaire pH2. La distribution de 1'Cnergie cinCtique des_atomes d'hydrogkne montre des preuves de la prCsence d'atomes provenant d'une photoIyse secondaire des fragments PH2(X) primaires. L'observation de cette photodissoc~ation secondaire dCmontre la prCsence d'une anisotropie marquCe qui est en accord avec une photoexcitation du fragment PH2(X). On prCsente des arguments indiquant que la photolyse secondaire conduit B la formation de fragments PH(X) portant des niveaux ClevCs d'excitation rotationnelle ainsi qu'au processus d'atomisation B trois corps.[Traduit par la redaction]

show abstract