Ayotte Lab
Our group is investigating physics and chemistry of ices. We use various surface science techniques to probe complex reaction dynamics as well as underlying mechanisms occurring in ice and at its surface. Through molecular modelling and numerical simulations, we endeavour to provide molecular level interpretations leading to a better understanding of environmental problems such as heterogeneous chemistry phenomena occurring in the atmosphere.
Recent Publications
Constantin Krüger, Elina Lisitsin-Baranovsky, Oded Ofer, Pierre-Alexandre Turgeon, Jonathan Vermette, Patrick Ayotte, Gil Alexandrowicz A magnetically focused molecular beam source for deposition of spin-polarised molecular surface layers Journal Article The Journal of Chemical Physics, 149 (16), pp. 164201, 2018. @article{Krüger2018, title = {A magnetically focused molecular beam source for deposition of spin-polarised molecular surface layers}, author = {Constantin Krüger and Elina Lisitsin-Baranovsky and Oded Ofer and Pierre-Alexandre Turgeon and Jonathan Vermette and Patrick Ayotte and Gil Alexandrowicz}, doi = {10.1063/1.5048521}, year = {2018}, date = {2018-10-22}, journal = {The Journal of Chemical Physics}, volume = {149}, number = {16}, pages = {164201}, abstract = {Separating molecular spin isomers is a challenging task, with potential applications in various fields ranging from astrochemistry to magnetic resonance imaging. A new promising method for spin-isomer separation is magnetic focusing, a method which was shown to be capable of producing a molecular beam of ortho-water. Here, we present results from a modified magnetic focusing apparatus and show that it can be used to separate the spin isomers of acetylene and methane. From the measured focused profiles of the molecular beams and a numerical simulation analysis, we provide estimations for the spin purity and the significantly improved molecular flux obtained with the new setup. Finally, we discuss the spin-relaxation conditions which will be needed to apply this new source for measuring nuclear magnetic resonance signals of a single surface layer.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Separating molecular spin isomers is a challenging task, with potential applications in various fields ranging from astrochemistry to magnetic resonance imaging. A new promising method for spin-isomer separation is magnetic focusing, a method which was shown to be capable of producing a molecular beam of ortho-water. Here, we present results from a modified magnetic focusing apparatus and show that it can be used to separate the spin isomers of acetylene and methane. From the measured focused profiles of the molecular beams and a numerical simulation analysis, we provide estimations for the spin purity and the significantly improved molecular flux obtained with the new setup. Finally, we discuss the spin-relaxation conditions which will be needed to apply this new source for measuring nuclear magnetic resonance signals of a single surface layer. |
Pierre-Alexandre Turgeon, Jonathan Vermette, Gil Alexandrowicz, Yoann Peperstraete, Laurent Philippe, Mathieu Bertin, Jean-Hugues Fillion, Xavier Michaut, Patrick Ayotte Confinement Effects on the Nuclear Spin Isomer Conversion of H2O Journal Article The Journal of Physical Chemistry A, 121 (8), pp. 1571-1576, 2017. @article{Turgeon2017, title = {Confinement Effects on the Nuclear Spin Isomer Conversion of H2O}, author = {Pierre-Alexandre Turgeon and Jonathan Vermette and Gil Alexandrowicz and Yoann Peperstraete and Laurent Philippe and Mathieu Bertin and Jean-Hugues Fillion and Xavier Michaut and Patrick Ayotte}, doi = {10.1021/acs.jpca.7b00893}, year = {2017}, date = {2017-02-03}, journal = {The Journal of Physical Chemistry A}, volume = {121}, number = {8}, pages = {1571-1576}, abstract = {The mechanism for interconversion between the nuclear spin isomers (NSI) of H2O remains shrouded in uncertainties. The temperature dependence displayed by NSI interconversion rates for H2O isolated in an argon matrix provides evidence that confinement effects are responsible for the dramatic increase in their kinetics with respect to the gas phase, providing new pathways for o-H2O↔p-H2O conversion in endohedral compounds. This reveals intramolecular aspects of the interconversion mechanism which may improve methodologies for the separation and storage of NSI en route to applications ranging from magnetic resonance spectroscopy and imaging to interpretations of spin temperatures in the interstellar medium.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The mechanism for interconversion between the nuclear spin isomers (NSI) of H2O remains shrouded in uncertainties. The temperature dependence displayed by NSI interconversion rates for H2O isolated in an argon matrix provides evidence that confinement effects are responsible for the dramatic increase in their kinetics with respect to the gas phase, providing new pathways for o-H2O↔p-H2O conversion in endohedral compounds. This reveals intramolecular aspects of the interconversion mechanism which may improve methodologies for the separation and storage of NSI en route to applications ranging from magnetic resonance spectroscopy and imaging to interpretations of spin temperatures in the interstellar medium. |
Elina Lisitsin-Baranovsky, Sarah Delage, Oscar Sucre, Oren Ofer, Patrick Ayotte, Gil Alexandrowicz In Situ NMR Measurements of Vapor Deposited Ice Journal Article The Journal of Physical Chemistry C, 120 (44), pp. 25445-25450, 2016. @article{Lisitsin-Baranovsky2016, title = {In Situ NMR Measurements of Vapor Deposited Ice}, author = {Elina Lisitsin-Baranovsky and Sarah Delage and Oscar Sucre and Oren Ofer and Patrick Ayotte and Gil Alexandrowicz}, doi = {10.1021/acs.jpcc.6b08746}, year = {2016}, date = {2016-10-13}, journal = {The Journal of Physical Chemistry C}, volume = {120}, number = {44}, pages = {25445-25450}, abstract = {In situ NMR spin–lattice relaxation measurements were performed on several vapor deposited ices. The measurements, which span more than 6 orders of magnitude in relaxation times, show a complex spin–lattice relaxation pattern that is strongly dependent on the growth conditions of the sample. The relaxation patterns change from multitime scale relaxation for samples grown at temperatures below the amorphous–crystalline transition temperature to single exponential recovery for samples grown above the transition temperature. The slow-relaxation contribution seen in cold-grown samples exhibits a temperature dependence, and becomes even slower after the sample is annealed at 200 K. The fast-relaxation contribution seen in these samples, does not seem to change or disappear even when heating to temperatures where the sample is evaporated. The possibility that the fast relaxation component is linked to the microporous structures in amorphous ice samples is further examined using an environmental electron scanning microscope. The images reveal complex mesoscale microporous structures which maintain their morphology up to their desorption temperatures. These findings, support the possibility that water molecules at pore surfaces might be responsible for the fast-relaxation contribution. Furthermore, the results of this study indicate that the pore-collapse dynamics observed in the past in amorphous ices using other experimental techniques, might be effectively inhibited in samples which are grown by relatively fast vapor deposition.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In situ NMR spin–lattice relaxation measurements were performed on several vapor deposited ices. The measurements, which span more than 6 orders of magnitude in relaxation times, show a complex spin–lattice relaxation pattern that is strongly dependent on the growth conditions of the sample. The relaxation patterns change from multitime scale relaxation for samples grown at temperatures below the amorphous–crystalline transition temperature to single exponential recovery for samples grown above the transition temperature. The slow-relaxation contribution seen in cold-grown samples exhibits a temperature dependence, and becomes even slower after the sample is annealed at 200 K. The fast-relaxation contribution seen in these samples, does not seem to change or disappear even when heating to temperatures where the sample is evaporated. The possibility that the fast relaxation component is linked to the microporous structures in amorphous ice samples is further examined using an environmental electron scanning microscope. The images reveal complex mesoscale microporous structures which maintain their morphology up to their desorption temperatures. These findings, support the possibility that water molecules at pore surfaces might be responsible for the fast-relaxation contribution. Furthermore, the results of this study indicate that the pore-collapse dynamics observed in the past in amorphous ices using other experimental techniques, might be effectively inhibited in samples which are grown by relatively fast vapor deposition. |
Guillaume Marcotte, Patrick Marchand, Stephanie Pronovost, Patrick Ayotte, Carine Laffon, Philippe Parent Surface-Enhanced Nitrate Photolysis on Ice Journal Article The Journal of Physical Chemistry A, 119 (10), pp. 1996-2005, 2015. @article{Marcotte2015, title = {Surface-Enhanced Nitrate Photolysis on Ice}, author = {Guillaume Marcotte and Patrick Marchand and Stephanie Pronovost and Patrick Ayotte and Carine Laffon and Philippe Parent}, doi = {10.1021/jp511173w}, year = {2015}, date = {2015-02-11}, journal = {The Journal of Physical Chemistry A}, volume = {119}, number = {10}, pages = {1996-2005}, abstract = {Heterogeneous nitrate photolysis is the trigger for many chemical processes occurring in the polar boundary layer and is widely believed to occur in a quasi-liquid layer (QLL) at the surface of ice. The dipole-forbidden character of the electronic transition relevant to boundary layer atmospheric chemistry and the small photolysis/photoproduct yields in ice (and in water) may confer a significant enhancement and interfacial specificity to this important photochemical reaction at the surface of ice. Using amorphous solid water films at cryogenic temperatures as models for the disordered interstitial air–ice interface within the snowpack suppresses the diffusive uptake kinetics, thereby prolonging the residence time of nitrate anions at the surface of ice. This approach allows their slow heterogeneous photolysis kinetics to be studied, providing the first direct evidence that nitrates adsorbed onto the first molecular layer at the surface of ice are photolyzed more effectively than those dissolved within the bulk. Vibrational spectroscopy allows the ∼3-fold enhancement in photolysis rates to be correlated with the nitrates’ distorted intramolecular geometry, thereby hinting at the role played by the greater chemical heterogeneity in their solvation environment at the surface of ice than that in the bulk. A simple 1D kinetic model suggests (1) that a 3(6)-fold enhancement in photolysis rate for nitrates adsorbed onto the ice surface could increase the photochemical NO2 emissions from a 5(8) nm thick photochemically active interfacial layer by 30(60)%, and (2) that 25(40)% of the NO2 photochemical emissions to the snowpack interstitial air are released from the topmost molecularly thin surface layer on ice. These findings may provide a new paradigm for heterogeneous (photo)chemistry at temperatures below those required for a QLL to form at the ice surface.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Heterogeneous nitrate photolysis is the trigger for many chemical processes occurring in the polar boundary layer and is widely believed to occur in a quasi-liquid layer (QLL) at the surface of ice. The dipole-forbidden character of the electronic transition relevant to boundary layer atmospheric chemistry and the small photolysis/photoproduct yields in ice (and in water) may confer a significant enhancement and interfacial specificity to this important photochemical reaction at the surface of ice. Using amorphous solid water films at cryogenic temperatures as models for the disordered interstitial air–ice interface within the snowpack suppresses the diffusive uptake kinetics, thereby prolonging the residence time of nitrate anions at the surface of ice. This approach allows their slow heterogeneous photolysis kinetics to be studied, providing the first direct evidence that nitrates adsorbed onto the first molecular layer at the surface of ice are photolyzed more effectively than those dissolved within the bulk. Vibrational spectroscopy allows the ∼3-fold enhancement in photolysis rates to be correlated with the nitrates’ distorted intramolecular geometry, thereby hinting at the role played by the greater chemical heterogeneity in their solvation environment at the surface of ice than that in the bulk. A simple 1D kinetic model suggests (1) that a 3(6)-fold enhancement in photolysis rate for nitrates adsorbed onto the ice surface could increase the photochemical NO2 emissions from a 5(8) nm thick photochemically active interfacial layer by 30(60)%, and (2) that 25(40)% of the NO2 photochemical emissions to the snowpack interstitial air are released from the topmost molecularly thin surface layer on ice. These findings may provide a new paradigm for heterogeneous (photo)chemistry at temperatures below those required for a QLL to form at the ice surface. |
