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X-ray photodesorption yields of N 2 15 and CO 13 are derived as a function of the incident photon energy near the N (∼400 eV) and O K-edge (∼500 eV) for pure N 2 15 ice and mixed CO 13 : N 2 15 ices. The photodesorption spectra from the mixed ices reveal an indirect desorption mechanism for which the desorption of N 2 15 and CO 13 is triggered by the photoabsorption of CO 13 and N 2 15 , respectively. This mechanism is confirmed by the x-ray photodesorption of CO 13 from a layered CO 13 / N 2 15 ice irradiated at 401 eV on the N 1s → π* transition of N 2 15 . This latter experiment enables us to quantify the relevant depth involved in the indirect desorption process, which is found to be 30–40 monolayers in that case. This value is further related to the energy transport of Auger electrons emitted from the photoabsorbing N 2 15 molecules that scatter toward the ice surface, inducing the desorption of CO 13 . The photodesorption yields corrected from the energy that can participate in the desorption process (expressed in molecules desorbed by eV deposited) do not depend on the photon energy; hence, they depend neither on the photoabsorbing molecule nor on its state after Auger decay. This demonstrates that x-ray induced electron stimulated desorption, mediated by Auger scattering, is the dominant process explaining the desorption of N 2 15 and CO 13 from the ices studied in this work. [ABSTRACT FROM AUTHOR]

Water molecules trapped in rare gas matrices exhibit conspicuous shifts in their far-infrared (FIR), rotranslational spectral features compared with the corresponding transitions observed in the gas phase. These confinement-induced perturbations have been related not only to the quantization of translational motion but also to the coupling between the orientational and positional degrees of freedom: the rotation–translation coupling (RTC). As the propensity displayed by the nuclear spin isomers (NSI) of water to undergo interconversion in confinement is intimately related to how its nuclear spin degrees of freedom are coupled with those for intra- and intermolecular motions, confinement-induced RTC should also strongly impact the NSI interconversion mechanisms and rates. Insight into the rotranslational dynamics for H 2 16 O , H 2 17 O , and H 2 18 O , confined in argon and krypton matrices, is provided here based on the evolution of rotranslational spectra induced by NSI interconversion while a definitive assignment is provided from the transition energies and intensities calculated using the confined rotor model [Paper I, Wespiser et al., J. Chem. Phys. 156, 074304 (2021)]. In order to build a complete rotranslational energy diagram of confined water, which is fundamental to understand the NSI interconversion rates, the energy difference between the ground ortho and para rotranslational states is derived from the temperature dependence of the intensity ratio of mid-infrared lines emerging from these states. These investigations should provide deeper insight of the factors that control NSI interconversion of water isotopologues under extreme confinement. [ABSTRACT FROM AUTHOR]

Core-excitation of water ice releases many different molecules and ions in the gas phase. Studying these desorbed species and the underlying desorption mechanisms can provide useful information on the effects of x-ray irradiation in ice. We report a detailed study of the x-ray induced desorption of a number of neutral, cationic, and anionic species from amorphous solid water. We discuss the desorption mechanisms and the relative contributions of Auger and secondary electrons (x-ray induced electron stimulated desorption) and initial excitation (direct desorption) as well as the role of photochemistry. Anions are shown to desorb not just through processes linked with secondary electrons but also through direct dissociation of the core-excited molecule. The desorption spectra of oxygen ions (O+, OH+, H2O+, O−, and OH−) give a new perspective on their previously reported very low desorption yields for most types of irradiations of water, showing that they mostly originate from the dissociation of photoproducts such as H2O2. [ABSTRACT FROM AUTHOR]

In this paper, we have studied adsorption and thermal desorption of methanol CH3OH on graphite surface, with the specific aim to derive from experimental data quantitative parameters that govern the desorption, namely, adsorption energy Eads and prefactor of the Polanyi-Wigner law. In low coverage regime, these two values are interconnected and usually the experiments can be reproduced with any couple (Eads), which makes intercomparison between studies difficult since the results depend on the extraction method. Here, we use a method for determining independently the average adsorption energy and a prefactor value that works over a large range of incident methanol coverage, from a limited set of desorption curves performed at different heating rates. In the low coverage regime the procedure is based on a first order kinetic law, and considers an adsorption energy distribution which is not expected to vary with the applied heating rate. In the case of CH3OH multilayers, Eads is determined as 430 meV with a prefactor of 5 × 1014 s-1. For CH3OH submonolayers on graphite, adsorption energy of 470 ± 30 meV and a prefactor of (8 ± 3) × 1016 s-1 have been found. These last values, which do not change between 0.09 ML and 1 ML initial coverage, suggest that the methanol molecules form island-like structure on the graphite even at low coverage. [ABSTRACT FROM AUTHOR]

In this paper, we have studied adsorption and thermal desorption of methanol CH3OH on graphite surface, with the specific aim to derive from experimental data quantitative parameters that govern the desorption, namely, adsorption energy Eads and prefactor ν of the Polanyi-Wigner law. In low coverage regime, these two values are interconnected and usually the experiments can be reproduced with any couple (Eads, ν), which makes intercomparison between studies difficult since the results depend on the extraction method. Here, we use a method for determining independently the average adsorption energy and a prefactor value that works over a large range of incident methanol coverage, from a limited set of desorption curves performed at different heating rates. In the low coverage regime the procedure is based on a first order kinetic law, and considers an adsorption energy distribution which is not expected to vary with the applied heating rate. In the case of CH3OH multilayers, Eads is determined as 430 meV with a prefactor of 5 × 10(14) s(-1). For CH3OH submonolayers on graphite, adsorption energy of 470 ± 30 meV and a prefactor of (8 ± 3) × 10(16) s(-1) have been found. These last values, which do not change between 0.09 ML and 1 ML initial coverage, suggest that the methanol molecules form island-like structure on the graphite even at low coverage.