Vibrational spectroscopy and photodissociation of jet-cooled ammonia

Bach, Andreas; Hutchison, J. Matthew; Holiday, Robert J.; Crim, F. Fleming

doi:10.1063/1.1450550

Cited by 58 publications

(51 citation statements)

References 33 publications

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“…The photolysis of ammonia is a prototypical example of dissociation through a conical intersection between two electronic states, and its study has shaped many ideas about the dissociation involving a conical intersection [20][21][22][23][24][25][26][27][28][29]. The adiabatic decomposition of electronically excited NH 3 (Ã 1 A 00 2 ) produces a hydrogen atom and an electronically excited fragment NH Ã 2 (H þ NH 2 ( 2 A 1 )), and the nonadiabatic decomposition *Corresponding author.…”

Section: Introductionmentioning

confidence: 99%

Vibrationally mediated photodissociation of ammonia: product angular distributions from adiabatic and nonadiabatic dissociation

Hause¹,

Yoon²,

Crim³

2008

Molecular Physics

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Velocity map ion imaging of H atoms from the photodissociation of vibrationally excited ammonia molecules measures the angular distribution of the fragments from dissociation of the excited state symmetric N-H stretch (1 1 ) and the antisymmetric N-H stretch (3 1 ). For the symmetric stretching state, the high rotational energy NH 2 fragments recoil with an angular distribution whose maximum is parallel to the polarization direction of the lasers, and the low rotational energy fragments recoil with a perpendicular angular distribution. This behavior is similar to that observed for photodissociation from the origin (0 0 ) but with a larger range in the anisotropy parameter ( 2 ) caused by additional alignment in the two-photon excitation. The dissociation through the excited state antisymmetric N-H stretch produces primarily electronically excited products (NH Ã 2 þ H). The initial alignment of molecules in the antisymmetric stretching state is a combination of perpendicular alignment from the vibrational excitation and parallel alignment from the electronic excitation. Fitting the more complicated angular distributions for the NH Ã 2 channel requires a higher order term ( 4 ) that also varies with recoil energy to describe the angular distribution.

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Section: Introductionmentioning

confidence: 99%

Vibrationally mediated photodissociation of ammonia: product angular distributions from adiabatic and nonadiabatic dissociation

Hause¹,

Yoon²,

Crim³

2008

Molecular Physics

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“…Cut through the Ã -and X -state potential energy surfaces of ammonia. The barrier to predissociation in the Ã state is 2348 cm -1 (see ref 17) Initial vibrational excitation changes the Franck-Condon factors for the subsequent electronic transition markedly, and we assign sharp resonances to a progression in the degenerate bending mode for the first time. Our assignment reveals an accidental degeneracy of the umbrella (2 1 ) and bending mode (4 1 ) with fundamental frequencies of 892 ( 8 and 906 ( 30 cm -1 , respectively.…”

Section: Introductionmentioning

confidence: 99%

“…The assignments are discussed in detail in ref17. The arrows show the total energies used to obtain Doppler profiles.…”

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confidence: 99%

Competition between Adiabatic and Nonadiabatic Pathways in the Photodissociation of Vibrationally Excited Ammonia

et al. 2003

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Vibrationally mediated photodissociation combined with Doppler spectroscopy and time-of-flight detection of H-atoms provides information on the photofragmentation dynamics from selected rovibrational states of Ã 1 A 2 ′′-state ammonia. The competition between adiabatic dissociation forming excited-state NH 2 ( 2 A 1 ) + H and nonadiabatic dissociation leading to ground-state NH 2 ( 2 B 1 ) + H products changes drastically for dissociation from different parent levels prepared by double-resonance excitation. The H-atom speed distributions suggest that the nonadiabatic dissociation channel is the major pathway except for dissociation from the antisymmetric N-H stretching (3 1 ) parent level, which forms exclusively NH 2 ( 2 A 1 ) + H. The energy disposal depends strongly on the parent state with as little as 2% of the available energy channeled into translational energy for dissociation from the 3 1 state.

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“…More recent studies [16,17] used synchrotron radiation or other modern VUV sources. Spectroscopic control of dissociation by pumping vibrational modes with microwave photons was demonstrated in references [18][19][20].…”

Section: Introductionmentioning

confidence: 99%