Vibrationally mediated photodissociation of ammonia: The influence of N–H stretching vibrations on passage through conical intersections

Hause, Michael L.; Yoon, Young-Gui; Crim, F. Fleming

doi:10.1063/1.2363192

Cited by 75 publications

(109 citation statements)

References 27 publications

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“…The N = K a rotational states are labeled as red and green dots for ν 2 = 0 and 1, respectively. 18 Biesner et al, 14 Hause et al, 23 and Rodríguez et al, 26 at the total energy of 6.55 eV (the 0 0 state). (b) Comparison of the calculated H-translational energy distribution of the NH 2 (X̃2B 1 ) product with the experimental results of Biesner et al 14 and Rodríguez et al 26 at the total energy of 6.66 eV (the 2 1 state).…”

Section: * S Supporting Informationmentioning

confidence: 97%

Full-Dimensional Quantum State-to-State Nonadiabatic Dynamics for Photodissociation of Ammonia in its A-Band

Xie,

Ma,

Zhu

et al. 2014

J. Phys. Chem. Lett.

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Full-dimensional state-to-state quantum dynamics of the photodissociation of NH 3 (Ã1A 2 ″) is investigated on newly developed coupled diabatic potential energy surfaces. For the first time, the rovibrational distributions of the nonadiabatically produced NH 2 (X̃2B 1 ) product have been determined quantum mechanically. In agreement with experimental observations, NH 2 (X̃2B 1 ) produced from the 0 0 and 2 1 states of NH 3 (Ã1A 2 ″) was found to be dominated by its ground vibrational state with an N = K a propensity, shedding light on the quantum-stateresolved nonadiabatic dynamics facilitated by conical intersections and setting the stage for the elucidation of vibrationally mediated photodissociation.SECTION: Spectroscopy, Photochemistry, and Excited States T he breakdown of the Born−Oppenheimer approximation in molecular systems is responsible for many important chemical processes, including vision and photosynthesis. Conical intersections (CIs) are the primary cause for the failure of the Born−Oppenheimer approximation. 1−3 Advances in our understanding of nonadiabatic dynamics have relied heavily on prototypical systems where the electron−nuclear interactions can be accurately characterized. Photodissociation of small molecules provides such an ideal proving ground. 4,5 Indeed, we have recently demonstrated that state-to-state multichannel quantum nonadiabatic dynamics of the photodissociation of water in its second absorption band can be quantitatively understood by wave-packet dynamics on accurate coupled potential energy surfaces (PESs). 6−8The photodissociation of ammonia in its A-band, which has been the object of innumerable experimental and theoretical studies over the past 30 years, provides another archetypical example of nonadiabatic dynamics. 4 Its six internal degrees of freedom offer dynamical features richer than those in the triatomic water molecule. In addition to the adiabatic dissociation channel leading to the H + NH 2 (Ã2A 1 ) products, nonadiabatic dissociation of photoexcited NH 3 (Ã1A 2 ″) through a seam of CIs between the ground and first excited electronic states of NH 3 leads to the lower energy H + NH 2 (X̃2B 1 ) products. As a result, it serves as an attractive system to understand, at the state-to-state level, multidimensional nonadiabatic dynamics and an array of other important dynamical properties including tunneling, mode specificity, and intramolecular vibrational energy redistribution (IVR).It is well established that the A←X̃absorption spectrum of ammonia is dominated by a long progression corresponding to umbrella mode (2 n ) excitations, which are attributed to the pyramidal-to-planar transition. 9 The diffuse characteristic of the absorption peaks reflects strong predissociation on the excited electronic state due to a small barrier just outside the quasibound Franck−Condon (FC) region. Lifetimes of these

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Section: * S Supporting Informationmentioning

confidence: 97%

Full-Dimensional Quantum State-to-State Nonadiabatic Dynamics for Photodissociation of Ammonia in its A-Band

Xie,

Ma,

Zhu

et al. 2014

J. Phys. Chem. Lett.

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“…There is a growing body of experiments and calculations on molecules with conical intersections in which the influence of one or more conical intersections on internal conversion or decomposition pathways is apparent [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. We have demonstrated that vibrational excitation can alter the probability of a molecule passing through a conical intersection by changing the trajectory that carries the system into the intersection [20,21]. In general, preparing molecules in a selected vibrational state prior to electronic excitation can alter dissociation dynamics and pathways by allowing the photoexcitation step to reach normally inaccessible regions of the excited-state potential.…”

Section: Introductionmentioning

confidence: 99%

“…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%

“…Nonadiabatic dissociation dominates at low excitation energies and adiabatic dissociation is more important at higher energies. We have previously used sequential vibrational and electronic excitation to prepare selected vibrations in electronically excited ammonia and have shown that H atoms from decomposition of the antisymmetric N-H stretching vibrational state (3 1 ) have very little kinetic energy while those from decomposition of the symmetric stretching state (1 1 ) have recoil energies ranging up to the energetic limit [20,21]. Velocity map ion imaging is able to resolve rotational structure of the partner NH 2 fragments in the total recoil energy distribution and, thus, identify the products as either NH 2 or NH Ã 2 .…”

Section: Introductionmentioning

confidence: 99%

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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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“…The success in this triatomic prototype spurred additional experiments on four atom molecules, including isocyanic acid, HNCO, 21 acetylene, C 2 H 2 , and its deuterated isotopologue, C 2 HD, 22 and ammonia, NH 3 , and its single deutarated variants, NHD 2 and NH 2 D. 23,24 An even larger a) Electronic mail: ibar@bgu.ac.il.…”

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confidence: 99%

Communication: Mode-specific photodissociation of vibrationally excited pyrrole

Epshtein

Portnov

Rosenwaks

et al. 2011

The Journal of Chemical Physics

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Laser-based spectroscopies coupled with molecular beam techniques facilitated the monitoring of H fragments released in ultraviolet photodissociation of pre-excited isoenergetic vibrational levels of pyrrole. Most noticeably, there was an order of magnitude larger reactivity for an eigenstate primarily consisting of two quanta of ring deformation than for another with one quantum of symmetric C–H stretch. The dynamics, the intramolecular interactions controlling the energy flow, and the mode-selectivity within a medium-sized, ten atom molecule, is discussed.

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Vibrationally mediated photodissociation of ammonia: The influence of N–H stretching vibrations on passage through conical intersections

Cited by 75 publications

References 27 publications

Full-Dimensional Quantum State-to-State Nonadiabatic Dynamics for Photodissociation of Ammonia in its A-Band

Full-Dimensional Quantum State-to-State Nonadiabatic Dynamics for Photodissociation of Ammonia in its A-Band

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

Communication: Mode-specific photodissociation of vibrationally excited pyrrole

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