Kochubei Sergei

Tungsten Isotope-Specific UV-Photodecomposition of W(CO)₆ at 266 nm

The Journal of Physical Chemistry A

UV photodissociation of tungsten hexacarbonyl W(CO)₆ has been studied in the molecular beam conditions using time-of-flight mass spectrometry and velocity map imaging. Irradiation of W(CO)₆ by pulsed laser radiation at 266 nm results in the appearance of singly and doubly charged tungsten ions. The isotope composition of these ions deviates essentially from natural abundance with deviation being pulse energy-dependent. The velocity map images of the tungsten ions indicate proceeding of several, more than two, parallel channels (sequences of the one-photon processes) of photodissociation, giving rise to tungsten atoms. Isotope effect is assigned to appear in a one-photon bound–bound transition in W(CO) intermediate followed by its predissociation. In the model suggested, the final state of this transition is a vibronic state with excited vibrational mode of W–C stretching vibration. This vibrational excitation is responsible for isotopic shift in the location of the final state. The suggested model fits the observed isotopic composition quantitatively.

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

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

Chemical Physics Letters

Decomposition Pathways of Titanium Isopropoxide Ti(OⁱPr)₄: New Insights from UV-Photodissociation Experiments and Quantum Chemical Calculations

The Journal of Physical Chemistry A

The UV-photodissociation at 266 nm of a widely used TiO₂ precursor, titanium tetraisopropoxide (Ti(OⁱPr)₄, TTIP), was studied under molecular-beam conditions. Using the MS-TOF technique, atomic titanium and titanium(II) oxide (TiO) were detected among the most abundant photofragments. Experimental results were rationalized with the aid of quantum chemical calculations (DLPNO–CCSD(T) and DFT). Contrary to the existing data in the literature, the new four-centered acetone-elimination reaction was found to be the primary decomposition process of TTIP. According to computational results, the effective activation barrier of this channel was ∼49 kcal/mol, which was ∼13 kcal/mol lower than that of the competing propylene elimination. The former process, followed by the dissociative loss of an H atom, was a dominating channel of TTIP unimolecular decay. The sequential loss of isopropoxy moieties via these two-step processes was supposed to produce the experimentally observed titanium atoms. In turn, the combination of these reactions with propylene elimination can lead to another detected species, TiO. These results indicate that the existing mechanisms of TTIP thermal and photoinitiated decomposition in the chemical-vapor deposition (CVD) of titanium dioxide should be reconsidered.

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

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.

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

Quantum Yield and Mechanism of Singlet Oxygen Generation via UV Photoexcitation of O₂–O₂ and N₂–O₂ Encounter Complexes

The Journal of Physical Chemistry A

The mechanism and spectral dependence of the quantum yield of singlet oxygen O₂(a ¹Δ_g) photogenerated by UV radiation in gaseous oxygen at elevated pressure (32–130 bar) have been experimentally investigated within the 238–285 nm spectral region overlapping the range of the Wulf bands in the absorption spectrum of oxygen. The dominant channel of singlet oxygen generation with measured quantum yield up to about 2 is attributed to the one-quantum absorption by the encounter complexes O₂–O₂. This absorption gives rise to oxygen in the Herzberg III state O₂(A′ ³Δ_u), which is assumed to be responsible for singlet oxygen production in the relaxation process O₂(A′ ³Δ_u, υ) + O₂(X ³Σ_g^–) → O₂({a ¹Δ_g" {b ¹Σ_g⁺}) + O₂({a ¹Δ_g, υ = 0" {b ¹Σ_g⁺, υ = 0}) with further collisional relaxation of b to a state. This mechanism is deduced from the analysis of the avoiding crossing locations on the potential energy surface of colliding O₂–O₂ pair. The observed drop of the O₂(a ¹Δ_g) yield near spectral threshold for O₂ dissociation is explained by the competition between above relaxation and reaction giving rise to O₃ + O (O + O + O₂) supposed in literature. The quantum yield of O₂(a ¹Δ_g) formation from encounter complex N₂–O₂ measured at λ = 266 nm was found to be the same as that for O₂–O₂.

Ionic Pathways following UV Photoexcitation of the (HI)₂ van der Waals Dimer

The Journal of Physical Chemistry A

Photodissociation of the (HI)₂ van der Waals dimers at 248 nm and nearby wavelengths has been studied using time-of-flight mass spectrometry and velocity map imaging. I₂⁺ product ions with a translational temperature of 130 K and “translationally hot” I⁺ ions with an average kinetic energy of E_t = 1.24 ± 0.03 eV and angular anisotropy β = 1.92 ± 0.11 were detected as dimer-specific ionic photofragments. Velocity map images of the I₂⁺ and I⁺ species were found to be qualitatively similar to those observed in the case of photoexcitation of the (CH₃I)₂ dimer (J. Chem. Phys.2005, 122, 204301). As in the case of the (CH₃I)₂ dimer, the absence of neutral I₂-specific features in the ionic species images from (HI)₂ allows us to eliminate neutral molecular I₂ as a precursor of I⁺ and I₂⁺. Similar to the case of (CH₃I)₂, we deduce that the observed I₂⁺ ions are produced in their ²Π_3/2,g ground electronic state as a result of photodissociation of the ionized dimer (HI)₂⁺ + hν → I₂⁺ + .... The formation of “translationally hot” I⁺ ions is attributed to photodissociation of nascent vibrationally excited I₂⁺ with an average vibrational energy of 1.05 ± 0.10 eV. This vibrational excitation is explained by the nonequilibrium initial I−I distance in I₂⁺ arising in photodissociation of (HI)₂⁺ after prompt release of the light H atoms. On the basis of our ab initio calculated value for the I−I distance of (3.17 Å) in the (HI)₂⁺ precursor dimer, the vibrational excitation of I₂⁺ is expected to be 1.02 eV, which is in quantitative agreement with our experimentally deduced value. The interpretation of our results was supported by ab initio calculations of the structure and energy of neutral and ionized dimers of HI at the MP4(SDTQ)//MP2 level.

Pulsed source of metal atoms and their compounds

Review of Scientific Instruments

UV photodissociation of the van der Waals dimer (CH₃I)₂ revisited: Pathways giving rise to ionic features

The Journal of Chemical Physics

Senior Researcher

Publications

Tungsten Isotope-Specific UV-Photodecomposition of W(CO)₆ at 266 nm

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

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

Decomposition Pathways of Titanium Isopropoxide Ti(OⁱPr)₄: New Insights from UV-Photodissociation Experiments and Quantum Chemical Calculations

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

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

Quantum Yield and Mechanism of Singlet Oxygen Generation via UV Photoexcitation of O₂–O₂ and N₂–O₂ Encounter Complexes

Ionic Pathways following UV Photoexcitation of the (HI)₂ van der Waals Dimer

Pulsed source of metal atoms and their compounds

UV photodissociation of the van der Waals dimer (CH₃I)₂ revisited: Pathways giving rise to ionic features

Kochubei Sergei

Senior Researcher

Publications

Tungsten Isotope-Specific UV-Photodecomposition of W(CO)6 at 266 nm

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

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

Decomposition Pathways of Titanium Isopropoxide Ti(OiPr)4: New Insights from UV-Photodissociation Experiments and Quantum Chemical Calculations

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(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

Quantum Yield and Mechanism of Singlet Oxygen Generation via UV Photoexcitation of O2–O2 and N2–O2 Encounter Complexes

Ionic Pathways following UV Photoexcitation of the (HI)2 van der Waals Dimer

Pulsed source of metal atoms and their compounds

UV photodissociation of the van der Waals dimer (CH3I)2 revisited: Pathways giving rise to ionic features

Tungsten Isotope-Specific UV-Photodecomposition of W(CO)₆ at 266 nm

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

Decomposition Pathways of Titanium Isopropoxide Ti(OⁱPr)₄: New Insights from UV-Photodissociation Experiments and Quantum Chemical Calculations

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

Quantum Yield and Mechanism of Singlet Oxygen Generation via UV Photoexcitation of O₂–O₂ and N₂–O₂ Encounter Complexes

Ionic Pathways following UV Photoexcitation of the (HI)₂ van der Waals Dimer

UV photodissociation of the van der Waals dimer (CH₃I)₂ revisited: Pathways giving rise to ionic features