Singlet Oxygen 1 O2 in Photocatalysis on TiO2 . Where Does It Come from? The Journal of Physical Chemistry C
Аннотация Подробнее Features of the near-infrared phosphorescence of singlet oxygen 1 O2 photosensitized by
TiO2 in solutions have been investigated. The short-lived phosphorescence of 1 O2
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 H2 O. The shorter lifetime and spectral shift
of this phosphorescence, as compared with phosphorescence of 1 O2 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 H2 O, respectively. The formation of 1 O2 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 H2 O 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 1 O2 in Photocatalysis on TiO2 . Where Does It Come from?” The Journal of Physical Chemistry C
Аннотация Подробнее 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 H2 O. 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 1 O2 . 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 1 O2 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
Аннотация Подробнее A broadband near-IR photodetector based on a large-area G12180-250A InGaAs photodiode (Hamamatsu) with a 5-mm-diameter
photosensitive area was developed and tested. It is designed for detecting the IR luminescence of singlet oxygen.
A circuit for signal amplification is assembled on the basis of broadband low-noise operational amplifiers with the
subsequent filtering of a signal with an adjustable passband f f f varied from 15 to 600 kHz, thus allowing one to obtain
a time resolution of better than 1 μ \mu μ s, a sensitivity level of 107− - − 109 V/W, and a noise equivalent
power NEP [W/Hz1/2 ] ≈ 1.4 x 10-14 λ \lambda λ -1 [μ \mu μ m] f f f [kHz] in a frequency band of 15− - − 600 kHz.
An Automated Apparatus for Measuring Spectral Dependences of the Mass Spectra and Velocity Map Images of Photofragments Instruments and Experimental Techniques
Аннотация Подробнее An automated apparatus is presented that allows a user to measure the mass spectrum
or velocity map images of photofragments during tuning of the dye-laser radiation wavelength and
its second harmonic, which interact with an investigated substance in a molecular beam.
The NI LabVIEW environment was used for automation. The apparatus was successfully tested when studying
the resonant ionization of oxygen molecules. The automation software makes it possible to extend
the possibilities of measuring spectral dependences by creating additional modules without
modifying the existing program code.
REMPI detection of singlet oxygen 1 O2 arising from UV‑photodissociation of van der Waals complex isoprene-oxygen C5 H8 ‑O2 Chemical Physics Letters
Подробнее Photodissociation of van der Waals complexes of iodine X–I2 (X = I2 , C2 H4 ) via charge-transfer state: A velocity map imaging investigation
The Journal of Chemical Physics
Аннотация Подробнее The photodissociation of van der Waals complexes of iodine X–I2 (X = I2 , C2 H4 )
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 2 P1/2 .
In the case of C2 H4 –I2 , the C2 H4 molecules appear in
the triplet T1 electronic state. Conical intersection for corresponding BET process becomes
energetically accessible after partial twisting of C2 H4 + frame in
the excited CT state of complex. The C2 H4 (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 CH3 I-O2 Chemical Physics Letters
Аннотация Подробнее Photoexcitation of van der Waals (vdW) complex CH3 I-O2 has been studied with
velocity map imaging of I atoms arising in photodissociation. A new scheme of resonance-enhanced multiphoton
ionization of iodine atoms has been applied with simultaneous use of UV and VIS radiation. The measured kinetic
energy of I(2 P3/2 ) atoms indicates photogeneration of precursor CH3 I molecules
via complex-specific channel with excitation energy expected for double spin-flip transition in
complex CH3 I-O2 . The angular distribution for recoil directions of I(2 P3/2 )
atoms coming from vdW complexes also corresponds to that expected for double spin-flip transition.
Role of ion-pair states in the predissociation dynamics of Rydberg states of molecular iodine Physical Chemistry Chemical Physics
Аннотация Подробнее 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+ (3 P2 ) +
I− (1 S0 ),
of the 2nd tier correlating to I+ (3 P0 ) +
I− (1 S0 ), and of the
3rd tier correlating to I+ (1 D2 ) +
I− (1 S0 ).
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(5s2 5p4 6s1 ).
The channel generating I(2 P3/2 ) +
I(2 P1/2 ) 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
Аннотация Подробнее The channel of singlet oxygen O2 (1 Δg )
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 C2 H4 ,
1,3-butadiene C4 H6 , deuterated methyl iodide
CD3 I, benzene C6 H6
and water H2 O and for those investigated previously indicate the DSF
mechanism as a source of singlet oxygen. The formation of O2
(1 Δg ) is observed only when the energy of exciting
quantum is sufficient for DSF transition. Universally detected low vibrational excitation of
O2 (1 Δg ) arising in
the photodissociation of van der Waals complexes X–O2 indicates the DSF
mechanism as its source. For complex of ethylene
C2 H4 –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
C2 H4 –O2 can be explained
by the DSF but not by the CT mechanism.
Predissociation dynamics of lithium iodide The Journal of Chemical Physics
Аннотация Подробнее 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 VXA = 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 (a 1 Δg ) formation via UV-excitation of isoprene-oxygen C5 H8 –O2 encounter complexes in gas phase Chemical Physics Letters
Аннотация Подробнее Photogeneration of singlet oxygen O2 (a 1 Δg ) resulted from photoexcitation at
248 and 266 nm of isoprene-oxygen mixtures at elevated oxygen pressure has been investigated.
Pulse energy and oxygen pressure dependence of the singlet oxygen yield indicate one-quantum
photoexcitation of the encounter complex isoprene-oxygen C5 H8 –O2
as a source of O2 (a 1 Δg ).
Suggested mechanism of O2 (a 1 Δg ) photogeneration involves direct
excitation of complex with simultaneous change of both partner spins like that observed in van der Waals complex
C5 H8 –O2 [Vidma et al., J. Chem. Phys. 137 (2012) 054305]. Other supposed pathways
involve collision-induced photogeneration of Herzberg III state O2 (A ’3 Δg )
or triplet isoprene as the intermediates.
Predissociation of high-lying Rydberg states of molecular iodine via ion-pair states The Journal of Chemical Physics
Подробнее Oxygen-assisted enhancement of H atom UV-photogeneration from hydrocarbons in van der Waals complexes RH–O2 Chemical Physics Letters
Аннотация Подробнее The strong enhancement of H-atom UV-photogeneration is revealed in van der Waals complexes of
unsaturated hydrocarbons RH (RH=ethylene C2 H4 , propylene C3 H6 ,
butadiene C4 H6 , butene–2 C4 H8 ) with oxygen RH–O2 as
compared with the ‘free’ RH molecules. The results obtained indicate enhancement of H atom yield to be due
to one-quantum photoprocess 1 RH–3 O2 + hν → 3 RH∗
+ 3 O2 (1 O2 ) providing triplet RH molecules with
excitation level sufficient for dissociation.