title: Photochemistry of Nitrophenol Molecules and Clusters: Intra- vs Intermolecular Hydrogen Bond Dynamics.
abstract: We investigate both experimentally and theoretically the structure and photodynamics of nitrophenol molecules and clusters, addressing the question how the molecular photodynamics can be controlled by specific inter- and intramolecular interactions. Using quantum chemical calculations, we demonstrate the structural and energetic differences between clusters of 2-nitrophenol and 4-nitrophenol, using phenol as a reference system. The calculated structures are supported by mass spectrometry. The mass spectra of 2-nitrophenol clusters provide an evidence for a stacked structure compared to a strong O-H···O hydrogen bonding for 4-nitrophenol aggregates. We further investigate the photodynamics of nitrophenol molecules and clusters by means of velocity map imaging of the H-fragment generated upon 243 nm photodissociation. The experiments are complemented by ab initio calculations which demonstrate distinct photophysics of phenol, 2-nitrophenol, 4-nitrophenol. The measured H-fragment kinetic energy distributions (KEDs) from 2-nitrophenol molecules are compared to the KEDs from phenol. The comparison points to the intramolecular O-H···O hydrogen bond in 2-nitrophenol, stimulating fast internal conversion into the ground electronic state. This reaction channel is marked by exclusive appearance of slow statistical hydrogen fragments in 2-nitrophenol, which contrasts with fast hydrogen atoms observed for phenol. The photodissociation of 2-nitrophenol clusters yields a fraction of H-fragments with higher kinetic energies than the isolated molecules. These fragments originate from the caging effect in the clusters leading to multiphoton dissociation of molecules excited by the previous photons. We also propose a new ab initio based value for the O-H bond dissociation enthalpy in 2-nitrophenol (4.25 eV), which is in excellent agreement with the maximum measured H-fragment kinetic energy.
authors.affiliation: J. Heyrovský Institute of Physical Chemistry v.v.i., Academy of Sciences of the Czech Republic , Dolejškova 3, 18223 Prague, Czech Republic.|Department of Physical Chemistry, University of Chemistry and Technology Prague , Technická 5, Prague 6, Czech Republic.
authors.forename: Kateryna
authors.initials: K
authors.lastname: Grygoryeva
authors.affiliation: Department of Physical Chemistry, University of Chemistry and Technology Prague , Technická 5, Prague 6, Czech Republic.
authors.forename: Jakub
authors.initials: J
authors.lastname: Kubečka
authors.affiliation: J. Heyrovský Institute of Physical Chemistry v.v.i., Academy of Sciences of the Czech Republic , Dolejškova 3, 18223 Prague, Czech Republic.
authors.forename: Andriy
authors.initials: A
authors.lastname: Pysanenko
authors.affiliation: J. Heyrovský Institute of Physical Chemistry v.v.i., Academy of Sciences of the Czech Republic , Dolejškova 3, 18223 Prague, Czech Republic.
authors.forename: Jozef
authors.initials: J
authors.lastname: Lengyel
authors.affiliation: J. Heyrovský Institute of Physical Chemistry v.v.i., Academy of Sciences of the Czech Republic , Dolejškova 3, 18223 Prague, Czech Republic.|Department of Physical Chemistry, University of Chemistry and Technology Prague , Technická 5, Prague 6, Czech Republic.
authors.forename: Petr
authors.initials: P
authors.lastname: Slavíček
authors.affiliation: J. Heyrovský Institute of Physical Chemistry v.v.i., Academy of Sciences of the Czech Republic , Dolejškova 3, 18223 Prague, Czech Republic.
authors.forename: Michal
authors.initials: M
authors.lastname: Fárník