A velocity map imaging study of the photodissociation of the Ã state of ammonia

Rodríguez, J. D.; González, Marta González; Rubio-Lago, Luis; Bañares, Luis

doi:10.1039/c3cp53523a

Cited by 19 publications

(32 citation statements)

References 24 publications

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“…The conical intersection of these two PESs in the planar geometry is located at the longer N−H distance (≈1.7 Å), 5,6 determining the branching ratio of the product pathways. [2][3][4]7 A similar argument has been presented for the photodissociation dynamics of methylamine (CH 3 NH 2 ), which is the simplest ammonia-derivative species. 8−11 Methylamine has two types of σ-bonds to nitrogen (C−N and N−H), both of which are photodissociated in the S 0 → S 1 transition (the first absorption band in the region 190− 240 nm).…”

Section: ■ Introductionsupporting

confidence: 53%

“…The branching ratio between the electronically excited- and ground-state adiabatic pathways in the ammonia and CH 3 NH 2 photodissociations has been discussed in connection with the dynamics around the conical intersections in the long-range regions. Through theoretical and experimental investigations, the branching ratio of the NH 3 + h ν → NH 2 (Ã 2 A 1 )/NH 2 (X̃ 2 B 1 ) + H reaction was estimated at 0.06–0.35 − ,,, and depended on the photoinitiated vibronic band of NH 3 (Ã 1 A 1 ). For the N–H bond fission channel of CH 3 NH 2 , the generation of the CH 3 NH(Ã 2 A′) product was indicated in the H atom tagging measurement by Reed et al .…”

Section: Discussionmentioning

confidence: 99%

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Detection of the Excited-State NH₂ (Ã ²A₁) in the Ultraviolet Photodissociation of Methylamine

et al. 2016

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Ion-imaging and dispersed fluorescence spectroscopy are employed for the photodissociation dynamics study of methylamine in the photolysis wavelength range 205-213 nm. The methyl radical product is found to populate a wide range of ro-vibrational states, among which the CH fragment generated in the v = 0 state shows a bimodal kinetic energy distribution. The internal energy analysis of the NH counterproduct indicates that a lower kinetic energy component, which was observed only with the CH(v=0) fragment, energetically matches the electronically excited ÃA state. The dispersed fluorescence spectrum, whose band structure is assigned to the ÃA → X̃B transition, provides evidence of the CH(v=0) + NH(ÃA) pathway. The branching mechanism of the product pathway is discussed in terms of nuclear dynamics in the long-range region, where the conical intersection between the excited- and ground-state potential energy surfaces can play a significant role.

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Section: ■ Introductionsupporting

confidence: 53%

Section: Discussionmentioning

confidence: 99%

Detection of the Excited-State NH₂ (Ã ²A₁) in the Ultraviolet Photodissociation of Methylamine

et al. 2016

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“…A very similar phenomenon has been invoked in the A ˜state dissociation of ammonia 60,61 and analogies have been drawn with the novel ''roaming'' mechanism first reported over a decade ago. [62][63][64] The same idea has also been suggested to explain aspects of the excited state dynamics seen in thioanisole, 65 methylamine 66 and aniline. 67,68 In the absence of extensive multi-state dynamics simulations and also specifically targeted experimental measurements, the exact details of this process remain an open question for now.…”

Section: Discussionmentioning

confidence: 92%

Time-resolved photoionization spectroscopy of mixed Rydberg-valence states: indole case study

Zawadzki

Thompson

Burgess

et al. 2015

Phys. Chem. Chem. Phys.

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Time-resolved photoelectron imaging was used to study non-adiabatic relaxation dynamics in gas-phase indole following photo-excitation at 267 nm and 258 nm. Our data analysis was supported by various ab initio calculations using both coupled cluster and density functional methods. The highly differential energy- and angle-resolved information provided by our experimental approach provides extremely subtle details of the complex interactions occurring between several low-lying electronically excited states. In particular, new insight into the role and fate of the mixed Rydberg-valence 3s/πσ* state is revealed. This includes population residing on the excited state surface at large N-H separations for a relatively long period of time (∼1 ps) prior to dissociation and/or internal conversion. Our findings may, in part, be rationalized by considering the rapid evolution of this state's electronic character as the N-H stretching coordinate is extended - as extensively demonstrated in the supporting theory. Overall, our findings highlight a number of important general caveats regarding the nature of mixed Rydberg-valence excited states, their spectral signatures and detection sensitivity in photoionization measurements, and the evaluation of their overall importance in mediating electronic relaxation in a wide range of small model-chromophore systems providing bio-molecular analogues - a topic of considerable interest within the chemical dynamics community over the last decade.

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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: 98%

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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A velocity map imaging study of the photodissociation of the Ã state of ammonia

Cited by 19 publications

References 24 publications

Detection of the Excited-State NH₂ (Ã ²A₁) in the Ultraviolet Photodissociation of Methylamine

Detection of the Excited-State NH₂ (Ã ²A₁) in the Ultraviolet Photodissociation of Methylamine

Time-resolved photoionization spectroscopy of mixed Rydberg-valence states: indole case study

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

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A velocity map imaging study of the photodissociation of the Ã state of ammonia

Cited by 19 publications

References 24 publications

Detection of the Excited-State NH2 (Ã 2A1) in the Ultraviolet Photodissociation of Methylamine

Detection of the Excited-State NH2 (Ã 2A1) in the Ultraviolet Photodissociation of Methylamine

Time-resolved photoionization spectroscopy of mixed Rydberg-valence states: indole case study

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

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Detection of the Excited-State NH₂ (Ã ²A₁) in the Ultraviolet Photodissociation of Methylamine

Detection of the Excited-State NH₂ (Ã ²A₁) in the Ultraviolet Photodissociation of Methylamine