Effect of cluster environment on the electron attachment to 2-nitrophenol

Effect of cluster environment on the electron attachment to 2-nitrophenol (2NP) is studied in homogeneous 2NP clusters and heterogeneous clusters of 2NP, argon and water. The cluster environment significantly reduces fragmentation of 2NP after electron attachment. Parent cluster anions 2NPn- are primary reaction products in both, homogeneous and heterogeneous clusters. Non-dissociative electron attachment to homogeneous clusters proceeds at low energies <2 eV, presumably via dipole-supported states. In heterogeneous clusters, the interaction with low energy (<2 eV) electrons is shielded by the solvent. Surprisingly, the energetic threshold for the electron attachment rises with the number (n) of 2NP molecules in the cluster (2NP)n-. This rise can be either due to a strong change of the 2NP conformation induced by the cluster environment or due to the the competition with electron autodetachment after proton transfer that has been first observed by Allan in the formic acid dimer [M. Allan, Phys. Rev. Lett. 98, 123201 (2007)]. We observe the same threshold rise for complex Arm·(2NP)n- and H2O·(2NP)n- anions. This indicates that the electron attachment to 2-nitrophenol in cluster environment is more influenced by the solute − solute interaction compared to the solute − solvent interaction

Vibrationally mediated photodissociation dynamics of pyrrole

We investigate photodissociation of vibrationally excited pyrrole molecules in a velocity map imaging experiment with IR excitation of N–H bond stretching vibration v1 = 1, νIR= 3532 cm−1, and UV photodissociation at λUV= 243 nm. In the IR+UV experiment, the H-fragment signal is enhanced with respect to the 243 nm UV-only photodissociation due to a more favorable Franck-Condon factor for the vibrationally excited molecule. In the measured H-fragment kinetic energy distribution, the maximum of the fast peak in the IR+UV experiment is shifted by 0.23 eV compared to the UV-only photodissociation which corresponds to 53 % of the vibrational energy deposited into the fragment kinetic energy. We compare our results with an isoenergetic UV-only photodissociation at λUV= 224 nm. About 72 % of the total available energy, is released into the fragment kinetic energy in the IR+UV experiment, while it is only 61 % in the UV-only photodissociation. This can be substantiated by the coupling of the N–H bond stretching vibration into the kinetic energy of the departing H-fragment. We also probe the time-dependent dynamics by a nanosecond pump-probe experiment. The IR excitation enhances the N–H bond dissociation even when the UV photodissociation is delayed by 150 ns. This enhancement increases also the yield of the fast fragments at the position of the peak corresponding to the IR+UV excitation, i.e. even 150 ns after the IR vibrational excitation, the same amount of the IR excitation energy can be converted into the H-fragment velocity as immediately after the excitation

Photochemistry of Nitrophenol Molecules and Clusters: Intra- vs Intermolecular Hydrogen Bond Dynamics

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 <i>ab initio</i> 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 <i>ab initio</i> 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

Decomposition of Iron Pentacarbonyl Induced by Singly and Multiply Charged Ions and Implications for Focused Ion Beam-Induced Deposition

International audienceFocused ion beams are becoming important tools in nanofabrication.The underlying physical processes in the substrate were already explored for severalprojectile ions. However, studies of ion interaction with precursor molecules forbeam-assisted deposition are almost nonexistent. Here, we explore the interaction ofvarious projectile ions with iron pentacarbonyl. We report fragmentation patterns ofisolated gas-phase iron pentacarbonyl after interaction with 4He+ at a collisionenergy of 16 keV, 4He2+ at 16 keV, 20Ne+ at 6 keV, 20Ne4+ at 40 keV, 40Ar+ at 3 keV,40Ar3+ at 21 keV, 84Kr3+ at 12 keV, and 84Kr17+ at 255 keV. These projectiles coverinteraction regimes ranging from collisions dominated by nuclear stopping throughcollisions dominated by electronic stopping to soft resonant electron-captureinteractions. We report a surprising efficiency of Ne+ in the Fe(CO)5decomposition. The interaction with multiply charged ions results in a highercontent of parent ions and slow metastable fragmentation due to the electroncaptureprocess. The release of CO groups during the decomposition process seems to take off a significant amount of energy.The fragmentation mechanism may be described as Fe being trapped within a CO cluster