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Full-Dimensional Theory of Pair-Correlated HNCO Photofragmentation Laurent Bonnet, Roberto Linguerri, Majdi Hochlaf, Ounaies Yazidi, Philippe Halvick, and Joseph S. Francisco J. Phys. Chem. Lett., Just Accepted Manuscript • Publication Date (Web): 12 May 2017 Downloaded from http://pubs.acs.org on May 16, 2017

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The Journal of Physical Chemistry Letters

Full-Dimensional Theory of Pair-Correlated HNCO Photofragmentation L. Bonnet,∗,† R. Linguerri,‡ M. Hochlaf,∗,‡ O. Yazidi,¶ P. Halvick,† and J. S. Francisco§ †Institut des Sciences Moléculaires, Université de Bordeaux, CNRS, UMR 5255, 33405, Talence, France ‡Laboratoire Modélisation et Simulation Multi Echelle, Université Paris-Est, UMR 8208 CNRS, 5 Bd Descartes, 77454 Marne La Vallée, France ¶Laboratoire de Spectroscopie Atomique, Moléculaire et Applications, LR01ES09, Faculté des Sciences de Tunis, Université de Tunis El Manar, 2092 Tunis, Tunisia §Department of Chemistry, University of Nebraska-Lincoln, 433 Hamilton Hall, Lincoln, Nebraska 68588-0304, USA E-mail: [email protected]; [email protected]

Abstract

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Full-dimensional semiclassical dynamical calculations combining classical paths and Bohr quantization of product internal motions are reported for the prototype photofragmentation of isocyanic acid in the S1 state. These calculations allow to closely reproduce for the first time key features of state-of-the-art imaging measurements at photolysis wavelengths of 201 and 210 nm while providing insight into the underlying dissociation mechanism. Quantum scattering calculations being beyond reach for most polyatomic fissions, pair-correlated data on these processes are much more often measured than predicted. Our theoretical approach can be used to fill this gap.

Gaussian Binning applied to the Classical Trajectory Method provides full imaging of the HNCO photofragmentation in the excited S1 state.

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energy distributions (KEDs) for the NH(a1 ∆) + CO(X1 Σ+ ) channel using velocity map imaging (VMI), where CO was state-selectively detected by (2+1) resonance-enhanced multiphoton ionization (REMPI). They proved the predominance of the formation of the previous products following photon excitation at 210 nm, 25 with co-product NH(a1 ∆) ≡ 1 NH in the vibrational ground state. Rotational state distributions of 1 NH were deduced from the KEDs while state-resolved anisotropy parameters (APs) were deduced from angular distributions. They showed that the produced CO fragments are rotationally hot (with population up to jCO = 50) while 1 NH co-products are rotationally cold. Moreover, APs are negative, thus indicating that the photofragmentation of HNCO at 210 nm is mainly direct. More recently, they 26 repeated the analogous experiment at 201 nm, where 1 NH was stateselectively detected via REMPI, and arrived at the following conclusions: the vibrational state populations (VSPs) of CO are inverted for nearly all the rotational states of 1 NH in its vibrational ground state; APs are negative, showing once again the direct nature of the dissociation; rotational state distributions of CO in the vibrational ground state are bimodal. Zhang et al. 26 interpreted the bimodality as resulting from the involvement of two HNCO isomers (cis and trans) in the fragmentation dynamics. The goal of this letter is to theoretically reproduce this correlated information on HNCO photodissociation around 200 and 210 nm and provide insight into its underlying dynamics, in particular, questioning the speculated mechanism. The exact quantum treatment of the photodissociation dynamics of tetratomic molecular systems is at the capacity limit of today’s theoretical and numerical techniques. 27 This is particularly true for the title process, as four different atoms are involved and no symmetry can be used to converge calculations by means of reasonable basis sizes (not to mention the significant mass of the three second raw atoms that is a complicating factor). Therefore, we used the newly developed classical trajectory method (CTM) in a quantum spirit. 28

Isocyanic acid, HNCO, is the simplest molecule that contains H, C, N and O atoms, which are essential for life and major constituents of chemical species in chemistry and biology. Since its discovery in 1830, 1 HNCO has been identified in diverse media. For instance, this molecule is found in over sixty galactic sources and in nine external galaxies. 2,5–9 It is relatively highly abundant and it is suggested to be strongly involved in prebiotic chemistry occurring there. Especially, it is a major component of the photochemistry of building blocks of life (DNA bases and amino acids). Isocyanic acid has been identified in the atmosphere, 3,4 where its sources are from both anthropogenic and naturally occurring biomass burning. It is known to be toxic and easily dissolves in water, in particular in lungs (cigarettes 10,11 ), posing obvious health risks such as the development of atherosclerosis, cataracts, rheumatoid arthritis 10,12 and inflammations that can lead to cardiovascular disease. To-date, the health effects of isocyanic acid, its role in the atmosphere and its photochemistry are not fully known nor understood. The photochemistry of HNCO under UV radiations or in combustion sources is complex. Besides the importance of isocyanic acid in diverse fields (see above), its unimolecular decomposition processes represent benchmarks for tetratomic molecules evolution upon electronic excitation. Previous studies showed that around 200 and 210 nm wavelengths, considered further in this work, HNCO mainly dissociates in the first excited singlet state S1 , 13–22 leading to the electronically excited NH(a1 ∆) photofragment and CO(X1 Σ+ ). For lower optical excitations, however, internal conversion to the S0 ground state (X1 A′ (1 1 A)) through seams of conical intersections with the S1 state (1 A′′ (2 1 A)) leads to the photofragments H + NCO, 23,24 by spin-allowed unimolecular decay, or to NH(X3 Σ− ) + CO(X1 Σ+ ), after intersystem crossing and decomposition on the lowest triplet state potential. Up-to-date experimental investigations of HNCO photodissociation have been performed by Yang and co-workers. 25,26 In 2007, they 25 measured pair-correlated angular and kinetic


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This semiclassical approach proved to lead to nearly quantitative predictions for several bimolecular, unimolecular and vibrational predissociation processes. 28,29 As for photodissociations, CTM in a quantum spirit involves the three following steps: (i) selecting the set of initial conditions of trajectories from the Wigner distribution associated with the internal state of HNCO before the optical excitation; 30,31 (ii) running trajectories from these initial conditions up to the separated products; 31 and (iii) deducing from the final conditions the paircorrelated KEDs, VSPs and APs by applying Bohr quantization rule 32 to product vibrational motions. 28 This basic rule of quantum mechanics states in a language suited to the present problem that one should only take into account those classical trajectories reaching the products with integer vibrational actions. This has a significant influence on the final results when only a small number of vibrational states are available to the products, as is the case for the fragmentation of HNCO at 201 and 210 nm. On the other hand, between ten and several tenths of rotational states are available to the products for this process, so rotational motions need not be pseudo-quantized. Strict application of Bohr’s condition of quantization is, however, too restrictive from a numerical point of view and, instead, trajectories are usually assigned Gaussian statistical weights such that the closer the vibrational actions to integer values, the larger the weights. This procedure is known as Gaussian binning (GB) 28 and CTM in a quantum spirit will thus be called GB-CTM. Within the framework of bimolecular collisions, GB has been shown to be consistent 28 with the semiclassical theory of molecular collisions pioneered by Miller and Marcus. 33,34 More technical details on the GB-CTM calculations presented further below can be found in the Supporting Information (SI). The coordinate system used in this work is represented in Fig. 1.

Figure 1: Internal coordinates used for the description of the HNCO PES. γ is the dihedral angle around the NC bond (γ = π for the trans configuration). We also give the bodyfixed frame convention. should be taken into account. About two decades ago, Klossika and Schinke 14 built an S1 planar five-dimensional (5D) potential energy surface (PES) fitted to high-level ab-initio calculations (KS-PES). We thus took advantage of the availability of this high-quality KS-PES to which we added a contribution depending mainly on rN C and the dihedral angle γ, fitted to equation-of-motion coupled-cluster calculations. This modification is detailed in the SI. Panel A in Fig. 2 displays the bi-dimensional cut of the resulting 6D-PES along rN C and the α angle, together with two typical trajectories discussed later below. Panel B in Fig. 2 shows a similar cut along rN C and the γ torsional angle (for both figures, the remaining coordinates were kept at the values corresponding to the trans minimum in the S1 state, given in Table V of ref. 14). It is worth noting that rN C and γ are strongly coupled to each other, which necessarily modifies the dynamics as compared to those obtained in a planar description. The GB-CTM KEDs at 210 nm are compared with their experimental counterparts in Fig. 3 (solid lines). These distributions are deduced from slicing images of CO in the vibrorotational states (nCO , jCO ) = (0,30) and (0,35). 25 The energy available to the products is such that 1 NH can only be in the vibrational ground state. The contributions assigned to the jN H rotational levels are also shown (dashed curves). As a matter of fact, the main features of the experimental KEDs (threshold and cut-off kinetic

None of the previous theoretical treatments of the title reaction were performed in fulldimensionality. 14,25 Instead, HNCO was kept planar throughout its fragmentation. For the sake of realism, however, out-of-plane motions


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ner (last) turning point is fairly similar to the red path. If all the trajectories were like the two previous ones, the rotational distribution would be a relatively narrow unimodal peak centered at jCO ≈ 30 − 35. However, part of the trajectories appear to be deflected by the potential wall lying on the right-side of the mountain pass en route to the product valley (see Fig. 2; this region is approximately defined by rN C within [3.8, 4.8] and α below 90 ◦ ). This is, for instance, slightly the case of the red path. This deflection, if strong enough, may make the final direction of the trajectories nearly parallel to the rN C axis of Fig. 2A, leading thereby to a rotationally cold CO. Consequently, the strong initial impulsion and the subsequent deflection create the large peak and the smaller bump, respectively, as is clearly visible in the lower panels of Fig. 4. In summary, the theoretical dynamics of the photofragmentation HNCO −→ NH(a1 ∆) + CO(X1 Σ) at 201 and 210 nm have been examined, assuming this process entirely takes place in the S1 state. Specifically, accurate semiclassical trajectory calculations on a new 6DPES have been carried out. The pair-correlated KEDs and APs measured by Yang and coworkers, 25,26 following state-selective detection of either CO or 1 NH via REMPI, have been calculated. The positions, widths and shapes of the KEDs are in good agreement with the experimental ones for most CO or 1 NH states probed. The APs are also in satisfying agreement with experiment, though the perpendicular polarization of the angular distributions is slightly overestimated by theory. On the other hand, we found that VSDs at 201 nm do not involve any inversion, in contrast with those deduced from the experimental KEDs. 26 However, experimentally deduced VSDs are necessarily equivocal when the co-product stateresolved components of the KEDs overlap, as is the case at 201 nm, whereas the theoretical determination of the VSDs is unambiguous. We thus see no contradiction between our results and the measurements of Yang and coworkers. 26 Last but not least, theory precludes the possibility of any link between the existence of two cis and trans HNCO isomers and the

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bimodality observed in the KEDs, as speculated in ref. 26. Instead, our treatment shows that bimodality should be the consequence of an impulsive-deflective mechanism due to two repulsive walls of the 6D-PES, the first one producing rotationally hot CO products, the second one cooling part of them. These findings provide new insights into the dissociation dynamics of the title tetratomic prototype fragmentation. At the moment, pair-correlated KEDs, VSPs and APs for dissociations involving more than three atoms have been much more often measured than theoretically predicted. In this regard, the present work fills an important gap ensuring the synergy between experiment and theory for these complex processes. This work can be straightforwardly extended to the description of state-to-state photodynamics through imaging techniques for polyatomics playing crucial roles in atmospheric and environmental chemistry. Supporting Information Available: In the Supporting Information, we detail the construction of the 6D-PES and the dynamical calculations of kinetic and rotational energy distributions, vibrational state populations and anisotropy parameters. This material is available free of charge via the Internet at http: //pubs.acs.org/. Acknowledgement We would like to thank Dr. Gustavo A. Garcia (Synchrotron Soleil, France) for fruitful discussions.

References (1) Liebig, J.; Wöhler, F. Untersuchungen über die Cyansäure. Ann. Phys. 1830, 96, 369-400. (2) Marcelino, N.; Brünken, S.; Cernicharo, J.; Quan, D.; Roueff, E.; Herbst, E.; Thaddeus, P. The Puzzling Behavior of HNCO Isomers in Molecular Clouds. A&A 2010, 516, A105-A112. (3) Perry, R. A.; Siebers, D. L. Rapid Reduc-


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(13) Zyrianov, M.; Droz-Georget, Th.; Reisler, H. Fragment Recoil Anisotropies in the Photoinitiated Decomposition of HNCO. J. Chem. Phys. 1999, 110, 2059-2068.

tion of Nitrogen Oxides in Exhaust Gas Streams. Nature 1986, 324, 657-658. (4) Miller, J. A.; Bowman, C. T. Kinetic Modeling of the Reduction of Nitric Oxide in Combustion Products by Isocyanic Acid. Int. J. Chem. Kinet. 1991, 23, 289-313.

(14) Klossika, J.-J.; Schinke, R. The Photodissociation of HNCO in the S1 Band: A Five-Dimensional Classical Trajectory Study. J. Chem. Phys. 1999, 111, 58825896.

(5) Snyder, L. E.; Buhl, D. Interstellar Isocyanic Acid. Astrophys. J. 1972, 177, 619623.

(15) Laine Berghout, H; Shizuka Hsieh; Fleming Crim, F. Relative Product Yields in the One-Photon and Vibrationally Mediated Photolysis of Isocyanic Acid (HNCO). J. Chem. Phys. 2001, 114, 10835-10844.

(6) Buhl, D.; Snyder, L. E.; Edrich, J. An Interstellar Emission Line from Isocyanic Acid at 1.4 Centimeters. ApJ 1972, 177, 625-628. (7) Zinchenko, I.; Henkel, C.; Mao, R. Q. HNCO in Massive Galactic Dense Cores. A&A 2000, 361, 1079-1094.

(16) Spiglanin, T. A.; Perry, R. A.; Chandler, D. W. Internal State Distributions of CO from HNCO Photodissociation. J. Chem. Phys. 1987, 87, 1568-1576.

(8) Nguyen-Q-Rieu; Henkel, C.; Jackson, J. M.; Mauersberger, R. Detection of HNCO in External Galaxies. A&A 1991, 241, L33-L36.

(17) Spiglanin, T. A.; Chandler, D. W. Rotational State Distributions of NH(a 1 ∆) from HNCO Photodissociation. J. Chem. Phys. 1987, 87, 1577-1581.

(9) Jackson, J. M.; Armstrong, J. T.; Barrett, A. H. HNCO in Molecular Clouds. ApJ 1984, 280, 608-614.

(18) Yi, W.; Bersohn, R. The Hydrogen Atom Channel in the Photodissociation of HNCO. Chem. Phys. Lett. 1993, 206, 365-368.

(10) Roberts, J. M.; Veres, P. R.; Cochran, A. K.; Warneke, C.; Burling, I. R.; Yokelson, R. J.; Lerner, B.; Gilman, J. B.; Kuster, W. C.; Fall, R.; de Gouw, J. Isocyanic Acid in the Atmosphere and its Possible Link to Smoke-Related Health Effects. PNAS 2011, 108, 8966-8971.

(19) Brownsword, R. A.; Laurent, T.; Vatsa, R. K.; Volpp, H.-R.; Wolfrum, J. Branching Ratio for the H + NCO Channel in the 193 nm Photodissociation of HNCO. Chem. Phys. Lett. 1996, 249, 162-166.

(11) Bowman, C. T. Control of CombustionGenerated Nitrogen Oxide Emissions: Technology Driven by Regulation. 24th Symp. (Int.) Combust. 1992, 859-878.

(20) Brownsword, R. A.; Laurent, T.; Vatsa, R. K.; Volpp, H.-R.; Wolfrum, J. Photodissociation Dynamics of HNCO at 248 nm. Chem. Phys. Lett. 1996, 258, 164-170.

(12) Young, P. J.; Emmons, L. K.; Roberts, J. M.; Lamarque, J.-F.; Wiedinmyer, C.; Veres, P.; VandenBoer, T. C. Isocyanic Acid in a Global Chemistry Transport Model: Tropospheric Distribution, Budget, and Identification of Regions with Potential Health Impacts. J. Geophys. Res. 2012, 117, D10308-D10321.

(21) Brownsword, R. A.; Hillenkamp, M.; Laurent, T.; Vatsa, R. K.; Volpp, H.-R. Photodissociation Dynamics in the UV Laser Photolysis of DNCO: Comparison with HNCO. J. Chem. Phys. 1997, 106, 44364447.


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(22) Brownsword, R. A.; Hillenkamp, M.; Volpp, H.-R.; Vatsa, R. K. Gas Phase Photofragmentation Dynamics of HNCO/DNCO after Laser Excitation at 222 nm. Res. Chem. Intermed. 1999, 25, 339-349.

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in the Fragmentation of Triatomic Negative Ions: Monte Carlo Scheme for a Classical Trajectory Study. J. Chem. Phys. 1976, 65, 5453-5461. (31) Schinke, R. Photodissociation Dynamics (Cambridge University Press, Cambridge, 1993).

(23) Yarkony, D. R. Characterizing the Local Topography of Conical Intersections Using Orthogonality Constrained Parameters: Application to the Internal Conversion S1 →S0 in HNCO. J. Chem. Phys. 2001, 114, 2614-2622.

(32) Bohr, N. I. On the Constitution of Atoms and Molecules. Phil. Mag. 1913, 26, 1-25. (33) Miller, W. H. Classical S Matrix: Numerical Application to Inelastic Collisions. J. Chem. Phys. 1970, 53, 3578-3587.

(24) Yarkony, D. R. Intersecting Conical Intersection Seams in Tetra-Atomic Molecules: the S1 -S0 Internal Conversion in HNCO. Mol. Phys. 2001, 99, 1463-1467.

(34) Marcus, R. Theory of Semiclassical Transition Probabilities (S Matrix) for Inelastic and Reactive Collisions. J. Chem. Phys. 1971, 54, 3965-3979.

(25) Wang, H.; Liu, S.-L.; Liu, J.; Wang, F.Y.; Jiang, B.; Yang, X.-M. Photofragment Imaging of HNCO Decomposition at 210 nm: the Primary NH(a1 ∆)+CO(X1 Σ+ ) Channel. Chinese J. Chem. Phys. 2007, 20, 388-394.

(35) Bonnet, L.; Corchado, J. C.; EspinosaGarcia, J. Pair-Correlated Speed Distributions for the OH+CH4 /CD4 Reactions: Further Remarks on their Classical Trajectory Calculations in a Quantum Spirit. C. R. Chimie 2016, 19, 571-578.

(26) Zhang, Z.; Chen, Z.; Huang, C.; Chen, Y.; Dai, D.; Parker, D. H.; Yang, X. Imaging the Pair-Correlated HNCO Photodissociation: The NH(a1 ∆) + CO(X1 Σ) Channel. J. Phys. Chem. A 2014, 118, 2413-2418. (27) Xie, C.; Ma, J.; Zhu, X.; Zhang, D. H.; Yarkony, D. R.; Xie, D.; Guo, H. Full-Dimensional Quantum State-to-State Nonadiabatic Dynamics for Photodissociation of Ammonia in its A-Band. J. Phys. Chem. Lett. 2014, 5, 1055-1060. (28) Bonnet, L. Classical Dynamics of Chemical Reactions in a Quantum Spirit. Int. Rev. Phys. Chem. 2013, 32, 171-228. (29) Shen, Z.; Ma, H.; Zhang, C.; Fu, M.; Wu, Y.; Bian, W.; Cao, J. Dynamical Importance of van der Waals Saddle and Excited Potential Surface in C(1 D)+D2 ComplexForming Reaction. Nat. Commun. 2017, 8, 14094-14100. (30) Goursaud, S.; Sizun, M.; Fiquet-Fayard, F. Energy Partitioning and Isotope Effects


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