Autoionization and isotope effect in the threshold photoelectron spectrum of 12CO2 and 13CO2

Formation of H3O+ and OH by CO2 and N2O trace gases in the atmospheric environment

The impact of cosmic rays' energetic subatomic particles on climate and global warming is still controversial and under debate. Cosmic rays produce ions that can trigger fast reactions affecting chemical networks in the troposphere and stratosphere especially when a large amount of relevant trace gases such as carbon dioxide, methane, sulfur dioxide and water are injected by volcanic eruptions. This work focuses on synchrotron experiments and an ab initio theoretical study of the ion chemistry of carbon dioxide and nitrous oxide radical cations reacting with water. These molecules catalyze a fast exothermic formation of hydronium ions H3O+ and the hydroxyl radical OH, the main oxidant in the atmosphere. Moreover, theoretical calculations demonstrate that at the end of the catalytic cycle, CO2 and N2O are produced vibrationally excited and subsequently they quench in the microsecond time scale by collision with the surrounding atmospheric molecules at the pressure and temperature of the upper-troposphere/stratosphere. The chemistry involved in these reactions has a strong impact on the oxidant capacity of the atmosphere, on the sulfate aerosol production, on the cloud formation and eventually on the chemical networks controlling climate and global warming models.

High resolution vibronic state-specific dissociation of NO2+in the 10.0–15.5 eV energy range by synchrotron double imaging photoelectron photoion coincidence

Low-lying electronic states of NO₂⁺are prepared with vibrational structures and their state-specific dissociation mechanisms are unraveled with high-resolution i²PEPICO.

State-Selected Reactivity of Carbon Dioxide Cations ( CO 2 + ) With Methane

The reactivity ofCO 2 + with CD4 has been experimentally investigated for its relevance in the chemistry of plasmas used for the conversion of CO2 in carbon-neutral fuels. Non-equilibrium plasmas are currently explored for their capability to activate very stable molecules (such as methane and carbon dioxide) and initiate a series of reactions involving highly reactive species (e.g., radicals and ions) eventually leading to the desired products. Energy, in the form of kinetic or internal excitation of reagents, influences chemical reactions. However, putting the same amount of energy in a different form may affect the reactivity differently. In this paper, we investigate the reaction ofCO 2 + with methane by changing either the kinetic energy ofCO 2 + or its vibrational excitation. The experiments were performed by a guided ion beam apparatus coupled to synchrotron radiation in the VUV energy range to produce vibrationally excited ions. We find that the reactivity depends on the reagent collision energy, but not so much on the vibrational excitation ofCO 2 + . Concerning the product branching ratios (CD 4 + /CD 3 + /DOCO+) there is substantial disagreement among the values reported in the literature. We find that the dominant channel is the production ofCD 4 + , followed by DOCO+ andCD 3 + , as a minor endothermic channel.

Photoionization studies of reactive intermediates using synchrotron radiation

Photoionization with synchrotron radiation enables sensitive and selective monitoring of reactive intermediates in environments such as flames and plasmas.

Advances in threshold photoelectron spectroscopy (TPES) and threshold photoelectron photoion coincidence (TPEPICO)

The history and evolution of molecular threshold photoelectron spectroscopy and threshold photoelectron photoion coincidence spectroscopy (TPEPICO) over the last fifty years are reviewed.

The X+ 2Πg, A+ 2Πu, B+ 2Δu, and a+ 4Σu(-) electronic states of Cl2(+) studied by high-resolution photoelectron spectroscopy

Partially rotationally resolved pulsed-field-ionization zero-kinetic-energy photoelectron spectra of the three isotopomers ((35)Cl2, (35)Cl(37)Cl, and (37)Cl2) of Cl2 have been recorded in the wavenumber ranges 92,500-96,500 cm(-1), corresponding to transitions to the low vibrational levels of the X(+) (2)Πg (Ω = 3∕2, 1∕2) ground state of Cl2 (+), and 106,750-115,500 cm(-1), where the a(+) (4)Σu (-)←X(1)Σg (+), A(+) (2)Πu←X(1)Σg (+), and B(+) (2)Δu←X(1)Σg (+) band systems overlap with transitions to high vibrational levels (v(+) > 25) of the X(+) state. The observation of Franck-Condon-forbidden transitions to vibrational levels of the X(+) state of the cation with v(+) ≥ 25 is rationalized by a mechanism involving vertical excitation of predissociative Rydberg states of mixed singlet-triplet character with an A(+) ion core which are coupled to Rydberg states converging to high-v(+) levels of the X(+) state. The same mechanism is proposed to also be responsible for the observation of Cl(+) - Cl(-) ion pairs and quartet states in the photoionization of Cl2. The potential energy function of the X(+) state of Cl2 (+) was determined in a direct fit to the experimental data. Transitions to vibrational levels of the A(+) (2)Πu, 3∕2 and B(+) (2)Δu, 3∕2 states of Cl2 (+) could be identified using the results of a recent analysis of the strong perturbation between the A(+) (2)Πu, 3∕2 and B(+) (2)Δu, 3∕2 states of Cl2 (+) observed in the A(+) - X(+) band system [Gharaibeh et al., J. Chem. Phys. 137, 194317 (2012)], and transitions to several vibrational levels of the upper spin-orbit component ((2)Πu, 1∕2) of the A(+) state were detected in the photoelectron spectrum of Cl2 (+). The a(+) (4)Σu (-)←X(1)Σg (+) photoelectron band system, which is nominally forbidden by single-photon ionization from the ground state was also observed for the first time and its vibrational and spin-orbit structures were analyzed. The (4)Σu (-) state is split into two spin-orbit components with Ω = 1∕2 and Ω = 3∕2, separated by 37.5 cm(-1). The vibrational energy level structure of both components is regular, which indicates that the splitting results from the interaction with one or more distant ungerade Ω = 1∕2 or Ω = 3∕2 electronic states.

Mode-specific photoelectron scattering effects on CO2+(C 2Σg+) vibrations

Using high-resolution photoelectron spectroscopy, we have determined the energy dependent vibrational branching ratios for the symmetric stretch [v+ = (100)], bend [v+ = (010)], and antisymmetric stretch [v+ = (001)], as well as several overtones and combination bands in the 4sigmag(-1) photoionization of CO2. Data were acquired over the range from 20-110 eV, and this wide spectral coverage highlighted that alternative vibrational modes exhibit contrasting behavior, even over a range usually considered to be dominated by atomic effects. Alternative vibrational modes exhibit qualitatively distinct energy dependences, and this contrasting mode-specific behavior underscores the point that vibrationally resolved measurements reflect the sensitivity of the electron scattering dynamics to well-defined changes in molecular geometry. In particular, such energy-dependent studies help to elucidate the mechanism(s) responsible for populating the symmetry forbidden vibrational levels [i.e., v+ =( 010), (001), (030), and (110)]. This is the first study in which vibrationally resolved data have been acquired as a function of energy for all of the vibrational modes of a polyatomic system. Theoretical Schwinger variational calculations are used to interpret the experimental data, and they indicate that a 4sigmag-->ksigmau shape resonance is responsible for most of the excursions observed for the vibrational branching ratios. Generally, the energy dependent trends are reproduced well by theory, but a notable exception is the symmetric stretch vibrational branching ratio. The calculated results display a strong peak in the vibrational branching ratio while the experimental data show a pronounced minimum. This suggests an interference mechanism that is not accounted for in the single-channel adiabatic-nuclei calculations. Electronic branching ratios were also measured and compared to the vibrational branching ratios to assess the relative contributions of interchannel (i.e., Herzberg-Teller) versus intrachannel (i.e., photoelectron-mediated) coupling.