Bogomolov Alexandr

Singlet Oxygen ¹O₂ in Photocatalysis on TiO₂. Where Does It Come from?

The Journal of Physical Chemistry C

Features of the near-infrared phosphorescence of singlet oxygen ¹O₂ photosensitized by TiO₂ in solutions have been investigated. The short-lived phosphorescence of ¹O₂ with spectral maximum at approximately 1300 nm is observed to follow excitation by pulsed laser radiation at 355 nm of TiO₂ suspended in CCl₄ and water H₂O. The shorter lifetime and spectral shift of this phosphorescence, as compared with phosphorescence of ¹O₂ sensitized by phenalenone in these solvents, are attributed to the adsorbed state of emitting singlet oxygen. The observed laser pulse energy dependence indicates the two-photon and three-photon nature of this phosphorescence initiation in CCl₄ and H₂O, respectively. The formation of ¹O₂ in CCl₄ is assumed to be provided by the sequence of one-photon excitation of TiO₂, giving rise to superoxide anion O₂^– and one-photon photodetachment of electron from O₂^–. The photodetachment of electron from O₂^– in water H₂O is a two-photon process because of higher solvation energy of superoxide anion in water. The processes that govern the rise and decay of singlet oxygen phosphorescence sensitized by TiO₂ are discussed. The factors affecting the yield of singlet oxygen provided by electron photodetachment are also considered.

Reply to Comments on “Singlet Oxygen ¹O₂ in Photocatalysis on TiO₂. Where Does It Come from?”

The Journal of Physical Chemistry C

In the Comment the authors Y. Nosaka and A. Y. Nosaka present arguments against the mechanism of singlet oxygen production which was suggested in the earlier published paper (Demyanenko et al., J. Phys. Chem. C 2019, 123, 2175) to explain the experimental data for the Near IR (NIR)-luminescence observed to appear after laser excitation at 355 nm of TiO₂ suspension in air-saturated solvents CCl₄ and H₂O. The main arguments of the Comment are directed against Assignment of the NIR Emission and Electron Photodetachment Mechanism suggested by Demyanenko et al.. Particularly the Comment claims that the red shift (near 30 nm) and bandwidth (50-60 nm) of the NIR luminescence observed in paper by Demyanenko et al. are too large to be assigned to the luminescence of singlet oxygen ¹O₂. In the Reply it is shown that several arguments of the Comment are based on the incorrect statements. The current interpretation of the nature of the red shift and bandwidth of the luminescence of singlet oxygen governed by interaction with the environment is considered. It is shown that the characteristics of NIR luminescence (rather large red shift and bandwidth as compared with the literature data for the luminescence of ¹O₂ in solutions) observed in experiments by Demyanenko et al. are in a qualitative agreement with expected tendencies. All the arguments of the Comment are considered in detail and extended reply is given.

A Broadband Near-IR Detector Based on a Large-Area InGaAs Photodiode for Time-Resolved Detection of Singlet Oxygen

Instruments and Experimental Techniques

An Automated Apparatus for Measuring Spectral Dependences of the Mass Spectra and Velocity Map Images of Photofragments

Instruments and Experimental Techniques

REMPI detection of singlet oxygen ¹O₂ arising from UV‑photodissociation of van der Waals complex isoprene-oxygen C₅H₈‑O₂

Chemical Physics Letters

Photodissociation of van der Waals complexes of iodine X–I₂ (X = I₂, C₂H₄) via charge-transfer state: A velocity map imaging investigation

The Journal of Chemical Physics

The photodissociation of van der Waals complexes of iodine X–I₂ (X = I₂, C₂H₄) excited via Charge-Transfer (CT) band has been studied with the velocity map imaging technique. Photodissociation of both complexes gives rise to translationally “hot” molecular iodine I₂ via channels differing by kinetic energy and angular distribution of the recoil directions. These measured characteristics together with the analysis of the model potential energy surface for these complexes allow us to infer the back-electron-transfer (BET) in the CT state to be a source of observed photodissociation channels and to make conclusions on the location of conical intersections where the BET process takes place. The BET process is concluded to provide an I₂ molecule in the electronic ground state with moderate vibrational excitation as well as X molecule in the electronic excited state. In the case of X = I₂, the BET process converts anion I₂⁻ of the CT state into the neutral I₂ in the repulsive excited electronic state which then dissociates promptly giving rise to a pair of I atoms in the fine states ²P_1/2. In the case of C₂H₄–I₂, the C₂H₄ molecules appear in the triplet T₁ electronic state. Conical intersection for corresponding BET process becomes energetically accessible after partial twisting of C₂H₄⁺ frame in the excited CT state of complex. The C₂H₄(T)–I₂ complex gives rise to triplet ethylene as well as singlet ethylene via the T-S conversion.

Oxygen-assisted excitation of methyl iodide as a test of double spin-flip transition in van der Waals complex CH₃I-O₂

Chemical Physics Letters

Role of ion-pair states in the predissociation dynamics of Rydberg states of molecular iodine

Physical Chemistry Chemical Physics

Using femtosecond pump–probe ion imaging spectroscopy, we establish the key role of I⁺ + I⁻ ion-pair (IP) states in the predissociation dynamics of molecular iodine I₂ excited to Rydberg states. Two-photon excitation of Rydberg states lying above the lowest IP state dissociation threshold (1st tier) is found to be followed by direct parallel transitions into IP states of the 1st tier asymptotically correlating to a pair of I ions in their lowest states I⁺(³P₂) + I⁻(¹S₀), of the 2nd tier correlating to I⁺(³P₀) + I⁻(¹S₀), and of the 3rd tier correlating to I⁺(¹D₂) + I⁻(¹S₀). Predissociation via the 1st tier proceeds presumably with a delay of 1.6–1.7 ps which is close to the vibrational period in the 3rd tier state (3rd tier-mediated process). The 2nd tier IP state is concluded to be the main precursor for predissociation via lower lying Rydberg states proceeding with a characteristic time of 7–8 ps and giving rise to Rydberg atoms I(5s²5p⁴6s¹). The channel generating I(²P_3/2) + I(²P_1/2) atoms with total kinetic energy corresponding to one-photon excitation is found to proceed via a pump – dump mechanism with dramatic change of angular anisotropy of this channel as compared with earlier nanosecond experiments.

Singlet oxygen photogeneration from X–O₂ van der Waals complexes: double spin-flip vs. charge-transfer mechanism

Physical Chemistry Chemical Physics

The channel of singlet oxygen O₂(¹Δ_g) photogeneration from van der Waals complexes of oxygen X–O₂ has been investigated to discriminate between two possible mechanisms based on charge-transfer (CT) or double spin-flip (DSF) transitions. The results obtained in this work for complexes with X = ethylene C₂H₄, 1,3-butadiene C₄H₆, deuterated methyl iodide CD₃I, benzene C₆H₆ and water H₂O and for those investigated previously indicate the DSF mechanism as a source of singlet oxygen. The formation of O₂ (¹Δ_g) is observed only when the energy of exciting quantum is sufficient for DSF transition. Universally detected low vibrational excitation of O₂(¹Δ_g) arising in the photodissociation of van der Waals complexes X–O₂ indicates the DSF mechanism as its source. For complex of ethylene C₂H₄–O₂ ab initio calculations of vertical energy ΔE_vert for DSF and CT transitions have been carried out. The positive results of singlet oxygen formation from C₂H₄–O₂ can be explained by the DSF but not by the CT mechanism.

Predissociation dynamics of lithium iodide

The Journal of Chemical Physics

The predissociation dynamics of lithium iodide (LiI) in the first excited A-state is investigated for molecules in the gas phase and embedded in helium nanodroplets, using femtosecond pump-probe photoionization spectroscopy. In the gas phase, the transient Li⁺ and LiI⁺ ion signals feature damped oscillations due to the excitation and decay of a vibrational wave packet. Based on high-level ab initio calculations of the electronic structure of LiI and simulations of the wave packet dynamics, the exponential signal decay is found to result from predissociation predominantly at the lowest avoided X-A potential curve crossing, for which we infer a coupling constant V_XA = 650(20) cm−1. The lack of a pump-probe delay dependence for the case of LiI embedded in helium nanodroplets indicates fast droplet-induced relaxation of the vibrational excitation.

Singlet oxygen O₂(a¹Δ_g) formation via UV-excitation of isoprene-oxygen C₅H₈–O₂ encounter complexes in gas phase

Chemical Physics Letters

Predissociation of high-lying Rydberg states of molecular iodine via ion-pair states

The Journal of Chemical Physics

Oxygen-assisted enhancement of H atom UV-photogeneration from hydrocarbons in van der Waals complexes RH–O₂

Chemical Physics Letters

Researcher

Education

Voevodsky Institute of Chemical Kinetics and Combustion of the Siberian Branch of the Russian Academy of Sciences

Novosibirsk State University

Publications

Singlet Oxygen ¹O₂ in Photocatalysis on TiO₂. Where Does It Come from?

Reply to Comments on “Singlet Oxygen ¹O₂ in Photocatalysis on TiO₂. Where Does It Come from?”

A Broadband Near-IR Detector Based on a Large-Area InGaAs Photodiode for Time-Resolved Detection of Singlet Oxygen

An Automated Apparatus for Measuring Spectral Dependences of the Mass Spectra and Velocity Map Images of Photofragments

REMPI detection of singlet oxygen ¹O₂ arising from UV‑photodissociation of van der Waals complex isoprene-oxygen C₅H₈‑O₂

Photodissociation of van der Waals complexes of iodine X–I₂ (X = I₂, C₂H₄) via charge-transfer state: A velocity map imaging investigation

Oxygen-assisted excitation of methyl iodide as a test of double spin-flip transition in van der Waals complex CH₃I-O₂

Role of ion-pair states in the predissociation dynamics of Rydberg states of molecular iodine

Singlet oxygen photogeneration from X–O₂ van der Waals complexes: double spin-flip vs. charge-transfer mechanism

Predissociation dynamics of lithium iodide

Singlet oxygen O₂(a¹Δ_g) formation via UV-excitation of isoprene-oxygen C₅H₈–O₂ encounter complexes in gas phase

Predissociation of high-lying Rydberg states of molecular iodine via ion-pair states

Oxygen-assisted enhancement of H atom UV-photogeneration from hydrocarbons in van der Waals complexes RH–O₂

Bogomolov Alexandr

Researcher

Education

Voevodsky Institute of Chemical Kinetics and Combustion of the Siberian Branch of the Russian Academy of Sciences

Novosibirsk State University

Publications

Singlet Oxygen 1O2 in Photocatalysis on TiO2. Where Does It Come from?

Reply to Comments on “Singlet Oxygen 1O2 in Photocatalysis on TiO2. Where Does It Come from?”

A Broadband Near-IR Detector Based on a Large-Area InGaAs Photodiode for Time-Resolved Detection of Singlet Oxygen

An Automated Apparatus for Measuring Spectral Dependences of the Mass Spectra and Velocity Map Images of Photofragments

REMPI detection of singlet oxygen 1O2 arising from UV‑photodissociation of van der Waals complex isoprene-oxygen C5H8‑O2

Photodissociation of van der Waals complexes of iodine X–I2 (X = I2, C2H4) via charge-transfer state: A velocity map imaging investigation

Oxygen-assisted excitation of methyl iodide as a test of double spin-flip transition in van der Waals complex CH3I-O2

Role of ion-pair states in the predissociation dynamics of Rydberg states of molecular iodine

Singlet oxygen photogeneration from X–O2 van der Waals complexes: double spin-flip vs. charge-transfer mechanism

Predissociation dynamics of lithium iodide

Singlet oxygen O2(a1Δg) formation via UV-excitation of isoprene-oxygen C5H8–O2 encounter complexes in gas phase

Predissociation of high-lying Rydberg states of molecular iodine via ion-pair states

Oxygen-assisted enhancement of H atom UV-photogeneration from hydrocarbons in van der Waals complexes RH–O2

Singlet Oxygen ¹O₂ in Photocatalysis on TiO₂. Where Does It Come from?

Reply to Comments on “Singlet Oxygen ¹O₂ in Photocatalysis on TiO₂. Where Does It Come from?”

REMPI detection of singlet oxygen ¹O₂ arising from UV‑photodissociation of van der Waals complex isoprene-oxygen C₅H₈‑O₂

Photodissociation of van der Waals complexes of iodine X–I₂ (X = I₂, C₂H₄) via charge-transfer state: A velocity map imaging investigation

Oxygen-assisted excitation of methyl iodide as a test of double spin-flip transition in van der Waals complex CH₃I-O₂

Singlet oxygen photogeneration from X–O₂ van der Waals complexes: double spin-flip vs. charge-transfer mechanism

Singlet oxygen O₂(a¹Δ_g) formation via UV-excitation of isoprene-oxygen C₅H₈–O₂ encounter complexes in gas phase

Oxygen-assisted enhancement of H atom UV-photogeneration from hydrocarbons in van der Waals complexes RH–O₂