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In the present work, the electronic structure and chemical bonding of the MoC X3Σ− ground state and the six lowest excited states, A3Δ, a1Γ, b5Σ−, c1Δ, d1Σ+, and e5Π, have been investigated in detail using multireference configuration interaction methods and basis sets, including relativistic effective core potentials. In addition, scalar relativistic effects have been considered in the second order Douglas–Kroll–Hess approximation, while spin–orbit coupling has also been calculated. Five of the investigated states, X3Σ−, A3Δ, a1Γ, c1Δ, and d1Σ+, present quadruple σ2σ2π2π2 bonds. Experimentally, the predissociation threshold of MoC was measured using resonant two-photon ionization spectroscopy, allowing for a precise measurement of the dissociation energy of the ground state. Theoretically, the complete basis set limit of the calculated dissociation energy with respect to the atomic ground state products, including corrections for scalar relativistic effects, De(D0), is computed as 5.13(5.06) eV, in excellent agreement with our measured value of D0(MoC) of 5.136(5) eV. Furthermore, the calculated dissociation energies of the states having quadruple bonds with respect to their adiabatic atomic products range from 6.22 to 7.23 eV. The excited electronic states A3Δ2 and c1Δ2 are calculated to lie at 3899 and 8057 cm−1, also in excellent agreement with the experimental values of DaBell et al., 4002.5 and 7834 cm−1, respectively. [ABSTRACT FROM AUTHOR]

Polycyclic aromatic hydrocarbons (PAHs) are common atmospheric pollutants, and they are also ubiquitous in the interstellar medium. Here, we report the study of a complex O-containing PAH anion, the deprotonated 2-hydroxytriphenylene (2-OtPh–), using high-resolution photoelectron imaging and photodetachment spectroscopy of cryogenically cooled anions. Vibrationally resolved photoelectron spectra yield the electron affinity of the 2-OtPh radical as 2.629(1) eV and several vibrational frequencies for its ground electronic state. Photodetachment spectroscopy reveals bound valence excited electronic states for the 2-OtPh– anion, with unprecedentedly rich vibronic features. Evidence is presented for a low-lying triplet state (T1) and two singlet states (S1 and S2) below the detachment threshold. Single-color resonant two-photon photoelectron spectroscopy uncovers rich photophysics for the 2-OtPh– anion, including vibrational relaxation in S1, internal conversion to the ground state of 2-OtPh–, intersystem crossing from S2 to T1, and a long-lived autodetaching shape resonance about 1.3 eV above the detachment threshold. The rich electronic structure and photophysics afforded by the current study suggest that 2-OtPh– would be an interesting system for pump–probe experiments to unravel the dynamics of the excited states of this complex PAH anion. [ABSTRACT FROM AUTHOR]

Carbon nanothreads are the most exciting carbon based nanomaterials recently discovered. Obtained by compressing aromatics around 20 GPa, they are characterized by potentially exceptional mechanical properties. The reaction mechanisms have been partly elucidated through computational studies and x-ray diffraction experiments. However, in all these studies, the electronic modifications to which the molecule is subjected with increasing pressure are neglected as also if, and to which extent, the electronic excited states are involved in the high-pressure reactivity. In fact, the pressure increase induces remarkable changes in the electronic properties of molecular crystals, which are often directly related to the reaction's onset and path. We report the pressure evolution of the two-photon induced emission spectrum of crystalline stilbene, the archetype of a class of molecules from which double-core nanothreads are obtained, with the twofold purpose of gaining insight into the reaction mechanism and monitoring if the structural changes observed in x-ray diffraction studies have a detectable counterpart in the electronic properties of the system. The freezing of the spectral diffusion observed on rising pressure is ascribed to a hampered conformational rearrangement because of the larger stiffness of the local environment. The transition to the high pressure phase where the nanothreads form is revealed by the slope change of the pressure shift of all spectral components, while the progressive intensification with pressure of the 0-0 transition suggests a strengthening of the ethylenic bond favoring the charge delocalization on the benzene moieties, which is likely the trigger of the chemical instability. [ABSTRACT FROM AUTHOR]

We present a compact laser system for quantitative two-photon excitation spectra measurements and ratiometric two-photon imaging of fluorescent protein indicators. The fundamental of the system is a short segment of photonic crystal fiber (PCF), which supports a nonlinear transformation of low-power ultrashort pulses by preserving temporal coherence, and this generates an ultrafast almost octave-spanning supercontinuum (SC). Accurate sculpting of the SC by its amplitude and phase modulation provides implementation of the spectroscopic and microscopic modalities. The spectroscopic one was exhibited by two-photon action cross section spectra measuring for the genetically encoded fluorescent sensing proteins of the vital biochemical parameters: acidity (SypHer3s), concentration of hydrogen peroxide (HyPer3 and HyPer7), redox status of NADH and glutathione (RexYFP and Grx1-roGFP2), hypohalous acids and their derivatives (Hypocrates). For the microscopy, we investigated and optimized the intensity pump pulse profiles under the high numerical objective by dispersion scan technique. We conducted real-time monitoring of the dynamics of hydrogen peroxide in HeLa cells with subcellular spatial resolution by means of ratiometric two-photon imaging of Hyper7 sensors. The presented hybrid laser system provides an ideal optical toolbox in order to develop ratiometric fluorescent sensors, which can be visualized in vivo using two-photon microscopy. [ABSTRACT FROM AUTHOR]

To assign cis and trans isomers of m-tolyl isocyanate (mTI) and p-phenylene diisocyanate (pPDI) in the electronic excitation transition, we measured the time-of-flight mass-selected resonant ionization spectra of jet-cooled phenyl isocyanate (PI), mTI, and pPDI in the region of the 275 nm first ππ* absorption system. In the excitation spectra of jet-cooled mTI and pPDI, cis- and trans-rotational isomers appeared as doublets. Isomers were assigned by analyzing the methyl-group internal rotation for mTI and by applying low-frequency bending vibrations to the mutual exclusion rule between the one- and two-photon spectra for pPDI. The electronic spectra of the three molecules observed in the jet were assigned to the transition to the first ππ* and third singlet excited states with the aid of time-dependent (TD)-B3LYP/aug-cc-pVDZ and TD-CAM-B3LYP/aug-cc-pVDZ calculations. The 0 − 0 band of PI was observed at 36 354 cm−1, those of the cis and trans isomers of mTI at 36 018 and 35 853 cm−1, respectively, and those of the cis and trans isomers of pPDI at 34 437 and 34 383 cm−1, respectively. All vibronic bands were diffuse, probably because of internal conversion to two singlet nπ* states. For mTI, based on changes in the barrier height of methyl-group internal rotation upon excitation, the Hammett-σm of PI was determined to be −0.12. [ABSTRACT FROM AUTHOR]

Two-photon ionization thresholds of RuB, RhB, OsB, IrB, and PtB have been measured using resonant two-photon ionization spectroscopy in a jet-cooled molecular beam and have been used to derive the adiabatic ionization energies of these molecules. From the measured two-photon ionization thresholds, IE(RuB) = 7.879(9) eV, IE(RhB) = 8.234(10) eV, IE(OsB) = 7.955(9) eV, IE(IrB) = 8.301(15) eV, and IE(PtB) = 8.524(10) eV have been assigned. By employing a thermochemical cycle, cationic bond dissociation energies of these molecules have also been derived, giving D0(Ru+–B) = 4.297(9) eV, D0(Rh+–B) = 4.477(10) eV, D0(Os–B+) = 4.721(9) eV, D0(Ir–B+) = 4.925(18) eV, and D0(Pt–B+) = 5.009(10) eV. The electronic structures of the resulting cationic transition metal monoborides (MB+) have been elucidated using quantum chemical calculations. Periodic trends of the MB+ molecules and comparisons to their neutral counterparts are discussed. The possibility of quadruple chemical bonds in all of these cationic transition metal monoborides is also discussed. [ABSTRACT FROM AUTHOR]

Excitation of vibration plays an important role in the photodissociation dynamics of molecules and ions. Experiments on the photodissociation dynamics of molecular ions via well-defined excited vibrational states present a formidable challenge, particularly when it comes to the selective preparation of ions at the vibrational combination level. Here, using time-sliced velocity map ion imaging, the photodissociation of H2S+ via A2A1(v1=1, v2=8, v3=0, K=1) state leading to S+(4S) and H2 products was investigated. The excited H2S+ cations were prepared by multiphoton ionization of H2S, followed by resonant excitation. Images of S+ ions were captured at six wavelengths ranging from 357.02 nm to 358.38 nm. From the ion images, the total kinetic energy release distributions and rotational state-specific anisotropy parameters were derived. Notably, repeatedly reversed branching ratios of the H2 (J=1) and H2 (J=3) rotational states were observed in a narrow photolysis energy region. This behavior was totally different from the results in recent studies on the photodissociation of HS+ where only a single vibrational mode v2 was excited for parent ions in A2A1(v1, v2, v3) states. The present study indicates that potential vibrational synergy effect was observed in the photodissociation dynamics of H2S+ when the parent ions were excited in a combinational vibrational mode. [ABSTRACT FROM AUTHOR]

Coherently controlling the spectral properties of energy-entangled photons is a key component of future entangled two-photon spectroscopy schemes that are expected to provide advantages with respect to classical methods. We present here an experimental setup based on a grating compressor. It allows for the spectral shaping of entangled photons with a sevenfold increase in resolution, compared to previous setups with a prism compressor. We evaluate the performances of the shaper by detecting sum frequency generation in a nonlinear crystal with both classical pulses and entangled photon pairs. The efficiency of both processes is experimentally compared and is in accordance with a simple model relating the classical and entangled two-photon absorption coefficients. Finally, the entangled two-photon shaping capability is demonstrated by implementing an interferometric transfer function. [ABSTRACT FROM AUTHOR]

We report an investigation of the 1-pyrenolate anion (PyO−) and the 1-pyrenoxy radical (PyO) using photodetachment spectroscopy and resonant photoelectron imaging of cryogenically cooled anions. The electron affinity of PyO is measured to be 2.4772(4) eV (19 980 ± 3 cm−1) from high-resolution photoelectron spectroscopy. Photodetachment spectroscopy reveals a dipole-bound state (DBS) for PyO− 280 cm−1 below the detachment threshold as well as a broad and intense valence excited state (shape resonance) 1077 cm−1 above the detachment threshold. The shape resonance with an excitation energy of 21 055 cm−1 is due to excitation of an electron from the highest occupied molecular orbital of PyO− to its lowest unoccupied molecular orbital in the continuum. Twenty-nine vibrational levels of the DBS are observed, including 27 above-threshold vibrational levels (vibrational Feshbach resonances). Twenty-seven resonant photoelectron spectra are obtained by tuning the detachment laser to the vibrational Feshbach resonances, resulting in highly non-Franck–Condon photoelectron spectra and rich vibrational information. In total, the frequencies of 21 vibrational modes are obtained for the PyO radical by the combination of the photodetachment and resonant photoelectron spectroscopy, including 13 out-of-plane bending modes. [ABSTRACT FROM AUTHOR]

The ground-state intermolecular dissociation energies D0(S0) of supersonic-jet cooled intermolecular complexes of 1-naphthol (1NpOH) with the bi- and tricycloalkanes trans-decalin, cis-decalin, and adamantane were measured using the stimulated-emission-pumping/resonant two-photon ionization (SEP-R2PI) method. Using UV/UV holeburning, we identified two isomers (A and B) of the adamantane and trans-decalin complexes and four isomers (A–D) of the cis-decalin complex. For 1NpOH·adamantane A and B, the D0(S0) values are 21.6 ± 0.15 kJ/mol and 21.2 ± 0.32 kJ/mol, those of 1NpOH·trans-decalin A and B are 28.7 ± 0.3 kJ/mol and 28.1 ± 0.9 kJ/mol, and those of 1NpOH·cis-decalin A and B are 28.9 ± 0.15 kJ/mol and 28.7 ± 0.3 kJ/mol. Upon S0 → S1 electronic excitation of the 1NpOH moiety, the dissociation energies of adamantane, trans-decalin, and the cis-decalin isomer C change by <1% and those of cis-decalin isomers A, B, and D increase only slightly (1%–3%). This implies that the hydrocarbons are dispersively adsorbed to a naphthalene "face." Calculations using the dispersion-corrected density functional theory methods B97-D3 and B3LYP-D3 indeed predict that the stable structures have face geometries. The B97-D3 calculated D0(S0) values are within 1 kJ/mol of the experiment, while B3LYP-D3 predicts D0 values that are 1.4–3.3 kJ/mol larger. Although adamantane has been recommended as a "dispersion-energy donor," the binding energies of the trans- and cis-decalin adducts to 1NpOH are 30% larger than that of adamantane. In fact, the D0 value of 1NpOH·adamantane is close to that of 1NpOH·cyclohexane, reflecting the nearly identical contact layer between the two molecules. [ABSTRACT FROM AUTHOR]

We report results for XUV-IR two-photon ionization of Ar, Ne, NO, and O2, where an XUV attosecond pulse train is superimposed with a synchronized IR pulse, obtained at the ATTOLab laser facility using electron–ion coincidence 3D momentum spectroscopy. Temporally resolved photoelectron angular distributions providing angle-resolved time-delays for np ionization of Ar and Ne, achieved by reconstruction of attosecond beating by interference of two-photon transitions through a unified formalism (Joseph et al. in J Phys B At Mol Opt Phys 53:184007, 2020), are summarized. For inner valence XUV-IR dissociative photoionization of NO and O2 molecules, we report electron–ion kinetic energy correlation diagrams and disentangle the dissociative photoionization processes relying on parallel XUV experiments at Synchrotron SOLEIL. For ionization into the NO+( c 3 Π ) ionic state, extending the formalism developed for single-photon ionization, we focus on photoelectron angular distributions averaged on the delay between the XUV and the IR field in the field frame, molecular frame, and electron frame of reference. [ABSTRACT FROM AUTHOR]

We study the interaction of a V-type atom in a cavity with incident single- and two-photon wavepackets and derive an exact formula, valid in all parameter regimes, relating the spectrum of the outgoing wavepackets to the incident one. We present detailed results for several special input pulses and consider the potential performance of the system as a CPHASE gate for initial pulses in a product state. We find values of the cavity, atomic, and pulse parameters that yield a conditional phase shift of π , albeit with a relatively small overlap between the incoming and outgoing pulse forms. [ABSTRACT FROM AUTHOR]

We present an experimental observation of 37D5/2 + 6S1/2Cs2 Rydberg-ground molecules by employing a two-photon photoassociation method. Two distinct Rydberg-ground molecular signals, deep and shallow bound molecules, are observed at the red detuning of atomic line. In theory, the model of scattering interaction between the Rydberg electron and ground-state atom is used to simulate the experiments. Two potential energy curves with energy minimum, deep pure triplet 3Σ and shallow hyperfine-mixed singlet–triplet 1,3Σ potentials, refer to the attained Rydberg-ground molecular signals, respectively. Calculations of the binding energy of triplet 3Σ and mixed 1,3Σ v = 0 states are compared with the measurements. The agreement between the calculated and measured values of the binding energy yields zero-energy scattering lengths a s T (0) = −19.2a0 and a s S (0) = −1.3a0, respectively. [ABSTRACT FROM AUTHOR]

The A ̃ 2 A 1 − X ̃ 2 B 1 electronic transition of the jet-cooled stibino (SbH2 and SbD2) free radical has been observed for the first time using laser induced fluorescence (LIF) detection. The radicals were produced by a pulsed electric discharge through a mixture of stibine (SbH3 or SbD3) in high pressure argon at the exit of a pulsed molecular beam valve. SbH2 exhibits only three LIF bands, assigned as 2 1 0 , 0 0 0 , and 2 0 1 , with a fluorescence lifetime (τ), which decreases from ∼50 ns for 00 to <10 ns for 21. LIF transitions to the 00 (τ ∼ 2 µs), 21 (τ ∼ 400 ns), and 22 (τ ∼ 75 ns) upper vibronic states of SbD2 were also observed. High-resolution spectra exhibited large spin-rotation splittings and small resolved antimony hyperfine splittings due to a substantial Fermi contact interaction in the excited state. The experimentally determined rotational constants gave effective molecular structures of r 0 ″ = 1.724(2) Å, θ 0 ″ = 90.38(7)° and r 0 ′ = 1.693(6) Å, θ 0 ′ = 120.6(3)°. The ground state bending vibrational levels up to eight quanta (6404 cm−1) in SbH2 and 12 quanta (6853 cm−1) in SbD2 were measured from dispersed fluorescence spectra. All indications are that SbH2 undergoes a dissociative process at low vibrational energies in the excited electronic state. [ABSTRACT FROM AUTHOR]

Vibronic spectroscopy and the S–H bond predissociation dynamics of 2-methoxythiophenol (2-MTP) in the S1 (ππ*) state have been investigated for the first time. Resonant two-photon ionization and slow-electron velocity map imaging (SEVI) spectroscopies have revealed that the S1–S0 transition of 2-MTP is accompanied with the planar to the pseudoplanar structural change along the out-of-plane ring distortion and the tilt of the methoxy moiety. The S1 vibronic bands up to their internal energy of ∼1000 cm−1 are assigned from the SEVI spectra taken via various S1 vibronic intermediate states with the aid of ab initio calculations. Intriguingly, Fermi resonances have been identified for some vibronic bands. The S–H bond breakage of 2-MTP occurs via tunneling through an adiabatic barrier under the S1/S2 conical intersection seam, and it is followed by the bifurcation into either the adiabatic or nonadiabatic channel at the S0/S2 conical intersection where the diabatic S2 state (πσ*) is unbound with respect to the S–H bond elongation coordinate, giving the excited (Ã) or ground ( X ̃ ) state of the 2-methoxythiophenoxy radical, respectively. Surprisingly, the nonadiabatic transition probability at the S0/S2 conical intersection, estimated from the velocity map ion images of the nascent D fragment from 2-MTP-d1 (2-CH3O–C6H4SD) at the S1 zero-point energy level, is found to be exceptionally high to give the X ̃ /Ã product branching ratio of 2.03 ± 0.20, which is much higher than the value of ∼0.8 estimated for the bare thiophenol at the S1 origin. It even increases to 2.33 ± 0.17 at the ν452 mode (101 cm−1) before it rapidly decays to 0.69 ± 0.05 at the S1 internal energy of about 2200 cm−1. This suggests that the strong intramolecular hydrogen bonding of S⋯D⋯OCH3 in 2-MTP at least in the low S1 internal energy region should play a significant role in localizing the reactive flux onto the conical intersection seam. The minimum energy pathway calculations (second-order coupled-cluster resolution of the identity or time-dependent-density functional theory) of the adiabatic S1 state suggest that the intimate dynamic interplay between the S–H bond cleavage and intramolecular hydrogen bonding could be crucial in the nonadiabatic surface hopping dynamics taking place at the conical intersection. [ABSTRACT FROM AUTHOR]

Predissociation thresholds of the ScSi, YSi, LaSi, ScC, YC, LaC, CoC, and YCH molecules have been measured using resonant two-photon ionization spectroscopy. It is argued that the dense manifold of electronic states present in these molecules causes prompt dissociation when the bond dissociation energy (BDE) is exceeded, allowing their respective predissociation thresholds to provide precise values of their bond energies. The BDEs were measured as 2.015(3) eV (ScSi), 2.450(2) eV (YSi), 2.891(5) eV (LaSi), 3.042(10) eV (ScC), 3.420(3) eV (YC), 4.718(4) eV (LaC), 3.899(13) eV (CoC), and 4.102(3) eV (Y–CH). Using thermochemical cycles, the enthalpies of formation, ΔfH0K°(g), were calculated as 627.4(9.0) kJ mol−1 (ScSi), 633.1(9.0) kJ mol−1 (YSi), 598.1(9.0) kJ mol−1 (LaSi), 793.8(4.3) kJ mol−1 (ScC), 805.0(4.2) kJ mol−1 (YC), 687.3(4.2) kJ mol−1 (LaC), 760.1(2.5) kJ mol−1 (CoC), and 620.8(4.2) kJ mol−1 (YCH). Using data for the BDEs of the corresponding cations allows ionization energies to be obtained through thermochemical cycles as 6.07(11) eV (ScSi), 6.15(13) eV (YSi), 5.60(10) eV (LaSi), 6.26(6) eV (ScC), 6.73(12) or 5.72(11) eV [YC, depending on the value of D0(Y+–C) employed], and 5.88(35) eV (LaC). Additionally, a new value of D0(Co+–C) = 4.045(13) eV was obtained based on the present work and the previously determined ionization energy of CoC. An ionization onset threshold allowed the measurement of the LaSi ionization energy as 5.607(10) eV, in excellent agreement with a prediction based on a thermochemical cycle. Chemical bonding trends are also discussed. [ABSTRACT FROM AUTHOR]

The stimulated-emission-pumping/resonant 2-photon ionization (SEP-R2PI) method was used to determine the intermolecular dissociation energies D0 of jet-cooled 1-naphthol(1NpOH)·S complexes, where S is a linear molecule (N2, CO, CO2, OCS, N2O, and ethyne) or symmetric-top molecule (2-butyne) that contains double or triple bonds. The dissociation energies D0(S0) are bracketed as follows: 6.68 ± 0.08 kJ/mol for S=N2, 7.7 ± 0.8 kJ/mol for CO, 12.07 ± 0.10 kJ/mol for CO2, 13.03 ± 0.01 kJ/mol for N2O, 14.34 ± 0.08 kJ/mol for ethyne, 15.0 ± 1.35 kJ/mol for OCS, and 29.6 ± 2.4 kJ/mol for 2-butyne. The minimum-energy structures, vibrational wavenumbers, and zero-point vibrational energies were calculated using the dispersion-corrected density functional theory methods such as B97-D3 and B3LYP-D3 with the def2-QZVPP basis set. These predict that N2 and CO are dispersively bound Face complexes (S bound to a naphthalene Face), while CO2, N2O, and OCS adsorb into the "Notch" between the naphthyl and OH groups; these are denoted as Notch complexes. Ethyne and 2-butyne form Edge complexes involving H-bonds from the —OH group of 1NpOH to the center of the molecule. The presence of a double or triple bond or an aromatic C=C bond within S does not lead to a specific calculated geometry (Face, Notch or Edge). However, a correlation exists between the structure and the sign of the quadrupole moment component Θzz of S: negative Θzz correlates with Face or Notch, while positive Θzz correlates with Edge geometries. [ABSTRACT FROM AUTHOR]

Graphene (G)-plasmonic nanoparticles (NPs) systems have found immense nanoscale applications via utilizing the sensitive optical response of graphene to the photo-induced electrons transferred from attached NPs. These electrons are emitted from the plasmonic metal NPs under the influence of a Localized Surface Plasmon Resonance (LSPR). Here, we first present theoretical investigations of the photoemission electrons in the G-plasmonic NPs system influenced by the LSPR of NPs. A rigorous theoretical approach is used to determine the level of photo-exited electrons and the optimal parameters for achieving a highest photoemission yield. The photoemission of electrons is mainly driven by the surface photoelectric effect in which an electron near the particle surface absorbs photon energy and overcomes the potential barrier at the metal–graphene boundary. For a thorough investigation, we study the effects of the material and geometry of NPs and the intensity of the LSPR field on the rate of photoemission. It is shown that silver nanoparticles combined with graphene are more effective in enhancing light–matter interaction in graphene owing to the lower interfacial energy barrier and higher field enhancement. Finally, we verify that the photo-induced electron density predicted by our calculations is matched with that obtained by combining theoretical and Raman-based experimental results. [ABSTRACT FROM AUTHOR]

We investigate a Dicke quantum battery in the dispersive regime, where the photons trapped in a resonant cavity are much more energetic with respect to the two-level systems embedded into it. Under such off-resonant conditions, even an empty cavity can lead to the charging of the quantum battery through a proper modulation of the matter–radiation coupling. This counterintuitive behaviour has its roots in the effective interaction between two-level systems mediated by virtual photons emerging from the fluctuations of the quantum electromagnetic field. In order to properly characterize it, we address relevant figures of merit such as the stored energy, the time required to reach the maximum charging, and the averaged charging power. Moreover, the possibility of efficiently extracting energy in various ranges of parameters is discussed. The scaling of stored energy and power as a function of the number N of two-level systems and for different values of the matter–radiation coupling is also discussed, showing, in the strong coupling regime, performances in line with what is reported for the Dicke quantum battery in the resonant regime. [ABSTRACT FROM AUTHOR]

26 Lin, Z., Simeone, D.M., Anderson, M.A., Brand, R.E., Xie, X., Shedden, K.A., Ruffin, M.T., and Lubman, D.M. Use of non-porous reversed-phase high-performance liquid chromatography for protein profiling and isolation of proteins induced by temperature variations for Siberian permafrost bacteria with identification by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and capillary electrophoresis-electrospray ionization mass spectrometry. 46 Nie, S., Yin, H., Tan, Z., Anderson, M.A., Ruffin, M.T., Simeone, D.M., and Lubman, D.M. 76 Zhu, J., He, J., Liu, Y., Simeone, D.M., and Lubman, D.M. [Extracted from the article]

Despite their global distribution moss physiology is not well understood, particularly in tropical environments. Photosynthetic Electron Transport Rate (ETR) of Hyophila involuta was measured using PAM technology. The plants were growing in a heavily shaded habitat with irregular sunflecks of full sunlight. Two models were used for estimating photosynthetic electron transport (ETR), the Waiting-in-Line and Eilers-Peeters models. Both take photoinhibition into account and gave similar results. The population studied was growing on bricks and stonework and so periodically dried out. The same species is sometimes found in waterfall environments where it is semi-aquatic. ETRmax was low at dawn, increased to an early morning maxima and then decreased during the course of the day, partially reversed by rainstorms. Mid-morning (10:30 solar time): Eopt ≈ 521 ± 77 µmol photon m–2 s–1 which is higher than might be expected in a shaded sun-fleck environment, ETRmax ≈ 28.3 ± 2.5 µmol e- m–2 s–1 on a projected surface area basis or ≈ 57.7 ± 5.1 (µmol e- g–1 Chl a s–1), photosynthetic efficiency (Alpha, α0) ≈ 0.301 (e- photon–1 g–1 Chl a). Chl a content of Hyophila was ≈ 453 mg Chl a m–2 with Chl b/a ≈ 0.371. The O2 electrode-based respiration rate was R = 6.78 ± 0.698 µmol O2 g–1 Chl a s–1, the ETRmax is roughly equivalent to Gross photosynthesis (Pg) ≈ 14.4 ± 1.28 µmol O2 g–1 Chl a s–1 (4 e-/ O2), so the optimum Pg/R ratio is about 2.12 ± 0.289 and net photosynthesis (Pn) is ≈ 7.62 ± 1.46 µmol O2 g–1 Chl a s–1. Thus even under optimum irradiance net photosynthesis was actually rather low. pH experiments showed that Hyophila used both CO2 & HCO3- inorganic carbon sources, suggesting that a concentrating mechanism (CCM) is present. Hyophila is partially homiochlorophyllous, recovering well from desiccation after 2h of lighted rehydration and recovers more after 24h but lost ≈30% of its Chl a. The moss retained its chlorophyll content if desiccated in the dark. The moss lost ≈ 2/3 of its Chl a during the monsoonal dry season. [ABSTRACT FROM AUTHOR]

The crystal structure of the title compound, C13H9Br2N [systematic name: (E)-N,1-bis­(4-bromo­phen­yl)methanimine], is a second polymorph (Form II) crystallizing in the ortho­rhom­bic space group Pccn. The first polymorph (Form I) crystallizes in the monoclinic space group P21/c [Bernstein & Izak (1975[Bernstein, J. & Izak, I. (1975). J. Cryst. Mol. Struct. 5, 257-266.]). J. Cryst. Mol. Struct. 5, 257-266; Marin et al. (2013[Marin, L., Harabagiu, V., van der Lee, A., Arvinte, A. & Barboiu, M. (2013). J. Mol. Struct. 1049, 377-385.]). J. Mol. Struct. 1049, 377-385]. The mol­ecule is disordered about an inversion center situated in the middle of the C=N bond, similar to the situation in the monoclinic polymorph: the C=N bond length is 1.243 (7) Å. In the crystal, mol­ecules stack along the b-axis direction and are linked by C--H π inter­actions. The inter­atomic contacts in the crystal for both polymorphs were studied by Hirshfeld surface analysis and have notable differences. The solid-state fluorescence spectrum of Form II shows an emission peak at ca 469 nm. The two-photon absorption coefficient measured from the open aperture Z-scan technique is 1.3 × 10-11 m W-1, hence, Form II shows optical limiting behaviour. [ABSTRACT FROM AUTHOR]

We study the Rabi flopping of the population between the ground and excited 2p states of the hydrogen atom, induced by intense short laser pulses of different shapes and of carrier frequency ω = 0.375 a.u. which resonantly couples the two states, and manifestations of this dynamics in the energy spectra of photoelectrons produced in the subsequent ionization of the atom from the excited state. It is found that, for Gaussian, half-Gaussian and rectangular pulses, characterized by the same pulse area, the final populations take the same values and the spectra consist of similar patterns having the same number of peaks and approximately the same separation between the prominent edge (Autler–Townes) peaks. The additional analysis in terms of dressed states showed that the mechanism of formation of multiple-peak structures during the photoionization process is the same regardless of the pulse shape. These facts disprove the hypothesis proposed in earlier studies with Gaussian pulse, that the multiple-peak pattern appears due to dynamic interference of the photoelectrons emitted with a time delay at the rising and falling sides of the pulse, since the hypothesis is not applicable to either a half-Gaussian pulse that has no rising part or a rectangular pulse whose intensity is constant. [ABSTRACT FROM AUTHOR]

The bound unoccupied electronic state structure of an Ir(111)/graphene surface covered by differently sized and spaced Ir clusters was investigated by means of two-photon photoemission spectroscopy. The cluster lattice was found to affect the image potential states of the substrate to a surprisingly large extent. This effect can be related to the influence of the cluster lattice on the screening of the image state electron trapped in front of the surface. The symmetric arrangement of Ir clusters considerably reduces the lateral extension of graphene areas with a homogeneous local work function, and from a certain minimum area size, the excitation of an electron to a stable state in a Coulomb-like potential is not possible anymore. Furthermore, lateral confinement effects could be observed due to the decreasing extension of bare graphene areas. [ABSTRACT FROM AUTHOR]

The 6 p 2 P 1 / 2 ← 6 s 2 S 1 / 2 and 6 p 2 P 3 / 2 ← 6 s 2 S 1 / 2 transitions (D lines) of gold atoms embedded in superfluid helium nanodroplets have been investigated using resonant two-photon ionization spectroscopy. Both transitions are strongly blue-shifted and broadened due to the repulsive interaction between the Au valence electron and the surrounding helium. The in-droplet D lines are superimposed by the spectral signature of Au atoms relaxed into the metastable 2D states. These features are narrower than the in-droplet D lines and exhibit sharp rising edges that coincide with bare atom transitions. It is concluded that they originate from metastable 2D state AuHen exciplexes that have been ejected from the helium droplets during a relaxation process. Interestingly, the mechanism that leads to the formation of these complexes is suppressed for very large helium droplets consisting of about 2 × 106 He atoms, corresponding to a droplet diameter on the order of 50 nm. The assignment of the observed spectral features is supported by ab initio calculations employing a multiconfigurational self-consistent field method and a multi-reference configuration interaction calculation. For large helium droplets doped with Au oligomers, excitation spectra for mass channels corresponding to Aun with n = 2, 3, 4, 5, 7, and 9 are presented. The mass spectrum reveals even-odd oscillations in the number of Au atoms that constitute the oligomer, which is characteristic for coinage metal clusters. Resonances are observed close by the in-droplet D1 and D2 transitions, and the corresponding peak forms are very similar for different oligomer sizes. [ABSTRACT FROM AUTHOR]

The antiferromagnetic Mott insulator α-Sr2CrO4 possesses multiple spin and orbital ordered phases, but their unique interplay is still relatively unexplored. Here, we used femtosecond optical spectroscopy to study ultrafast spin and orbital ordering dynamics in α-Sr2CrO4 through their non-equilibrium response to photoexcitation. By varying the pump photon energy, we selectively drove inter-site spin hopping between neighboring Cr t2g orbitals and charge transfer-type transitions between oxygen 2p and Cr eg orbitals. The resulting transient reflectivity dynamics revealed temperature-dependent anomalies across the Néel temperature for spin ordering as well as the transition temperatures linked to different types of orbital order. Our results reveal distinct relaxation timescales for spin and orbital orders in α-Sr2CrO4 and provide experimental evidence for the phase transition at TO, possibly related to antiferro-type orbital ordering. Strongly correlated electron systems, such as the chromates, can exhibit a range of unique electronic configurations, the phase diagram of which can become even richer when considering non-equilibrium properties. Here, the authors apply ultrafast optical spectroscopy to α-Sr2CrO4 in order to investigate its spin and orbital ordering dynamics and the changes that occur when varying the pump photon energy. [ABSTRACT FROM AUTHOR]

The antiferromagnetic Mott insulator α-Sr2CrO4 possesses multiple spin and orbital ordered phases, but their unique interplay is still relatively unexplored. Here, we used femtosecond optical spectroscopy to study ultrafast spin and orbital ordering dynamics in α-Sr2CrO4 through their non-equilibrium response to photoexcitation. By varying the pump photon energy, we selectively drove inter-site spin hopping between neighboring Cr t2g orbitals and charge transfer-type transitions between oxygen 2p and Cr eg orbitals. The resulting transient reflectivity dynamics revealed temperature-dependent anomalies across the Néel temperature for spin ordering as well as the transition temperatures linked to different types of orbital order. Our results reveal distinct relaxation timescales for spin and orbital orders in α-Sr2CrO4 and provide experimental evidence for the phase transition at TO, possibly related to antiferro-type orbital ordering. Strongly correlated electron systems, such as the chromates, can exhibit a range of unique electronic configurations, the phase diagram of which can become even richer when considering non-equilibrium properties. Here, the authors apply ultrafast optical spectroscopy to α-Sr2CrO4 in order to investigate its spin and orbital ordering dynamics and the changes that occur when varying the pump photon energy. [ABSTRACT FROM AUTHOR]

In this work, we present a scheme of a two-photon interaction to calculate magic wavelengths for the 6 2 S 1 2 − 5 2 D 3 2 , 5 2 clock transitions of Ba + ion employing the relativistic coupled-cluster method. These magic wavelengths can be essential inputs to achieve better accuracy in the future ionic clock experiments. In this paper, we further show an application of a two-photon interaction to the spin-mixing processes, | 0 , 0 〉 ↔ | + 1 , − 1 〉 and | 0 , 0 〉 ↔ | − 1 , + 1 〉 , of an ultra-cold spin-1 mixture of 137 Ba + ions and 87 Rb atoms. We determine the protocols for selecting these spin-mixing oscillations by changing the strength and frequencies of the externally applied magnetic field and laser beams, respectively. [ABSTRACT FROM AUTHOR]

The recent detection of urea in the interstellar medium raises questions about its stability in different astronomical environments. In this work, we have studied the stability of urea ices and urea/water ice mixtures under vacuum-ultraviolet (VUV; 6.3–10.9 eV) irradiation and high-energy (5 keV) electron bombardment at 30, 100, and 200 K. The evolution of the ices was monitored with infrared spectroscopy. CO2, HNCO, and OCN− were identified as reaction products in the 30 K samples. At the higher temperatures CO2 and HNCO were hardly found in the processed ices. The measurements provided destruction cross-sections and allowed the derivation of radiation yields, G 100, and half-life doses for urea. G 100 values were found to be low (≈3.6–0.3 molecules/100 eV) both for VUV photons and high-energy electrons with electrons being slightly more efficient for the destruction of the molecule. These low G 100 values are likely due to favourable mechanisms of energy dissipation or urea recombination. The stability of urea under irradiation increases with temperature which suggests that higher mobility improves the repair mechanisms. Estimates based on these laboratory data indicate that urea should be stable (≈108–109 yr) against irradiation in cold dense clouds and hot cores. It would not survive long (≈103–104 yr) on the bare surface of a Kuiper belt object, but would be well protected (≈109 yr) against radiation below a 30  |$\mu$| m ice layer. The high resistance of the molecule to radiation damage makes it a good candidate for prebiotic chemistry. [ABSTRACT FROM AUTHOR]

Keldysh ionization theory is one of the main pillars of strong field physics and attosecond science. It describes non-relativistic ionization rates of hydrogen-like atoms subjected to strong laser fields within the dipole approximation and the length gauge. According to this theory ionization can be described by two regimes: electronic tunneling through a laser-dressed atomic potential (tunnel ionization) and absorption of multiple photons at once (multi-photon ionization). There are many gaps in the mathematical steps and explanations in the original Keldysh paper. Therefore, the goal of this work is to give a detailed re-derivation of ionization rates following Keldysh’s formulation and to fill in the mathematical steps of this beautiful approach so that it is more accessible to a wider audience. [ABSTRACT FROM AUTHOR]

Two-photon absorption (2PA) spectra of several prototypical molecules (ethylene, toluene, trans- and cis-stilbene, and phenanthrene) are computed using the equation-of-motion coupled-cluster method with single and double substitutions. The states giving rise to the largest 2PA cross sections are analyzed in terms of their orbital character and symmetry-based selection rules. The brightest 2PAtransitions correspond to Rydberg-like states from fully symmetric irreducible representations. Symmetry selection rules dictate that totally symmetric transitions typically have the largest 2PA cross sections for an orientationally averaged sample when there is no resonance enhancement via one-photon accessible intermediate states. Transition dipole arguments suggest that the strongest transitions also involve the most delocalized orbitals, including Rydberg states, for which the relative transition intensities can be rationalized in terms of atomic selection rules. Analysis of the 2PA transitions provides a foundation for predicting relative 2PA cross sections of conjugated molecules based on simple symmetry and molecular orbital arguments. [ABSTRACT FROM AUTHOR]

Based on the quantum memory-assisted entropic uncertainty relation (QMA-EUR), we investigate the Markovian and non-Markovian dynamics of entanglement witness in a two-atom system that asymmetrically are coupled to a leaky cavity with two-photon relaxation. The atoms are two-level systems, they move inside the cavity and interact with a classical driving laser field. We discuss in detail the effects of the translational movement of the atoms, classical driving field and atom-cavity coupling on the protection of entanglement witness. Our results show that with a regular increase in the intensity of the classical driving field, the entanglement region witnessed by lower bound of QMA-EUR increases and the time of entanglement witness gets longer. In the Markovian regime, we find that quantum entanglement between the moving atoms can be witnessed for a longer time by increasing the velocity of the atoms. However, in the non-Markovian regime, higher speeds are required to witness entanglement over long time intervals. In addition, we conclude that the entanglement region witnessed by the lower bound of QMA-EUR can be protected in both the symmetrical and asymmetrical atom-cavity coupling regimes. In the asymmetrical regime, a better protection can be achieved when the memory atom is coupled to the cavity field stronger than the other atom. [ABSTRACT FROM AUTHOR]

Understanding in situ crystallization of perovskite materials is fundamentally important for perovskite‐based materials, components, and devices. Here, in situ crystallization of perovskites in three dimensions is investigated using two‐photon excitation fluorescence microscopy with diffraction‐limited spatial resolution. By taking a perovskite precursor droplet as an example, the spatiotemporal kinetics of nanocrystal formation during crystallization is demonstrated, taking advantage of the perovskites' unique advantage of in situ synthesis from solutions. Based on the time‐lapsed 3D two‐photon excitation fluorescence imaging, the in situ formation of the "crystal crust" is observed and the results suggest a centripetal direction of the crystallization starting from the free surface of the droplet. Analysis based on fluorescence intensity further confirms the evaporation kinetics in a sessile precursor droplet. The reported results demonstrate a promising framework for utilizing two‐photon excitation fluorescence microscopy as a powerful tool to study the in situ crystallization of perovskite materials as well as more general fluorescence‐related chemical reactions in three dimensions. [ABSTRACT FROM AUTHOR]

The effects of the non-ideality (NI) of classical plasmas on the photoionization of helium atoms at high non-relativistic photon energies are investigated within the framework of the dipole approximation. Screened interaction in non-ideal plasmas is represented by an effective potential, deduced from a solution of Bogolyubov's hierarchy equations on discarding the effects of quantum degeneracy. A highly correlated wave function consisting of 715 terms for the ground state of helium has been used to evaluate the dipole matrix element. Changes in the asymptotic cross sections of single, double, and total photoionizations due to varying NI of plasmas have been investigated in detail. Particular emphasis is made to study the changes in the asymptotic ratio of the double-to-single photoionization cross section caused by the variation of non-ideality parameter in a wide range. It is found that increasing plasma NI makes the feasibility of occurrence of double photoionization to broaden. [ABSTRACT FROM AUTHOR]

Most experimental methods for studying the kinetics of surface reactions – for example, temperature programmed desorption (TPD), molecular beam relaxation spectrometry (MBRS) and velocity‐resolved kinetics (VRK) – employ detection schemes that require thermal desorption. However, many adsorbates – for example reaction intermediates – never leave the surface under reaction conditions. In this paper, we present a new method to measure adsorbate concentrations on catalytic surfaces and demonstrate its utility for studying thermal desorption kinetics. After a short‐pulsed molecular beam deposits CO or NH3 on Pt (111), the surface is irradiated with an ultrashort laser pulse that induces desorption. Another tightly focused ultrashort laser pulse ionizes the gas‐phase molecules by a non‐resonant multiphoton process and the ions are detected. This two‐laser signal is then recorded as a function of time after the dosing molecular beam pulse and decays exponentially. First‐order thermal desorption rate constants are obtained over a range of temperatures and found to be in good agreement with past reports. Ion detection is done mass selectively with ion‐imaging, dispersing the gas phase molecules by their velocities. Since laser‐induced desorption (LID) produces hyperthermal gas phase molecules, they can be detected with little or no background. This approach is highly surface‐specific and exhibits sensitivity below 10−4 ML coverage. Because the signals are linearly proportional to adsorbate concentration, the method can be employed at lower temperatures than VRK, whose signal is proportional to reaction rate. [ABSTRACT FROM AUTHOR]

The first derivatives of the electronic moments of the transition along the coordinates, HT ht , were calculated numerically. For this, the Dirac distribution function I i in Eq. (1) is replaced by expression HT ht . Therefore, in practice, the Taylor series is used near the equilibrium geometry of the ground electronic state: HT ht Graph (2)where B I Q i b are mass-weighted normal coordinates. [Extracted from the article]

Interaction of atoms with twisted light is the subject of intense experimental and theoretical investigation. In almost all studies, the atom is viewed as a localized probe of the twisted light field. However, as argued in this paper, conceptually novel effects will arise if light‐atom interaction is studied in the double‐twisted regime with delocalized atoms, that is, either via twisted light absorption by atom vortex beam, or via two‐twisted‐photon spectroscopy of atoms in a non‐vortex but delocalized state. Even for monochromatic twisted photons and for an infinitely narrow line, absorption will occur over a finite range of detuning. Inside this range, a rapidly varying absorption probability is predicted, revealing interference fringes induced by two distinct paths leading to the same final state. The number, location, height, and contrast of these fringes can give additional information on the excitation process which would not be accessible in usual spectroscopic settings. Visibility of the predicted effects will be enhanced at the future Gamma factory thanks to the large momenta of ions. [ABSTRACT FROM AUTHOR]

Predissociation thresholds have been observed in the resonant two-photon ionization spectra of TiSe, ZrSe, HfSe, VSe, NbSe, and TaSe. It is argued that the sharp onset of predissociation corresponds to the bond dissociation energy in each of these molecules due to their high density of states as the ground separated atom limit is approached. The bond dissociation energies obtained are D0(TiSe) = 3.998(6) eV, D0(ZrSe) = 4.902(3)eV, D0(HfSe) = 5.154(4)eV, D0(VSe) = 3.884(3)eV, D0(NbSe) = 4.834(3)eV, and D0(TaSe)= 4.705(3)eV. Using these dissociation energies, the enthalpies of formation were found to be Δf,0KHo(TiSe(g)) = 320.6±16.8 kJ mol-1, Δf,0KHo(ZrSe(g)) = 371.1±8.5 kJ mol-1, Δf,0KHo(HfSe(g)) = 356.1 ± 6.5 kJ mol-1, Δf,0KHo(VSe(g)) = 372.9 ± 8.1 kJ mol-1, Δf,0KHo(NbSe(g)) = 498.9 ±8.1 kJ mol-1, and Δf,0KHo(TaSe(g)) = 562.9±1.5 kJ mol-1. Comparisons are made to previous work, when available. Also reported are calculated ground state electronic configurations and terms, dipole moments, vibrational frequencies, bond lengths, and bond dissociation energies for each molecule. A strong correlation of the measured bond dissociation energy with the radial expectation value, ⟨r⟩nd, for the metal atom is found. [ABSTRACT FROM AUTHOR]

Resonant two-photon threshold ionization spectroscopy is employed to determine the ionizationenergy of C2 to 5 meV precision, about two orders of magnitude more precise than the previously accepted value. Through exploration of the ionization threshold after pumping the 0-3 band of the newly discovered 4³Πg←a³Πu band system of C2, the ionizationenergy of the lowest rovibronic level of the a³Πu state was determined to be 11.791(5) eV. Accounting for spin-orbit and rotational effects, we calculate that the ionizationenergy of the forbidden origin of the a³Πu state is 11.790(5) eV, in excellent agreement with quantum thermochemical calculations which give 11.788(10) eV. The experimentally derived ionizationenergy of X¹Σg+X¹Σg+ state C2 is 11.866(5) eV. [ABSTRACT FROM AUTHOR]

Resonant two-photon threshold ionization spectroscopy is employed to determine the ionizationenergy of C2 to 5 meV precision, about two orders of magnitude more precise than the previously accepted value. Through exploration of the ionization threshold after pumping the 0-3 band of the newly discovered 4³Πg←a³Πu band system of C2, the ionizationenergy of the lowest rovibronic level of the a³Πu state was determined to be 11.791(5) eV. Accounting for spin-orbit and rotational effects, we calculate that the ionizationenergy of the forbidden origin of the a³Πu state is 11.790(5) eV, in excellent agreement with quantum thermochemical calculations which give 11.788(10) eV. The experimentally derived ionizationenergy of X¹Σg+X¹Σg+ state C2 is 11.866(5) eV. [ABSTRACT FROM AUTHOR]

Detection of O( 3 P j ) atoms using one-photon resonant excitation to the 3 s 3 S 1 o state at ∼ 130 nm followed by near-threshold ionisation, i.e. 1 + 1' resonance-enhanced multi-photon ionisation, has been investigated. The aim was to achieve low ion recoil, improved sensitivity, and reliable angular momentum polarisation information, with an as simple as possible laser setup. An efficient 1 + 1' scheme has been found where the VUV light for the first step is generated by difference frequency ( 2 ω 1 − ω 2 ) VUV generation, and the ionisation step 1' uses 2 ω 2 around 289 nm. The presented scheme induces 9 m/s recoil of the O + ion using a two-dye laser system, and zero recoil should be possible by generating 302 nm radiation with a third dye laser. While this approach is much more sensitive than a previous 1 + 1' scheme using 212.6 nm for the 1' step, we found that the relatively intense radiation of the 2 ω 2 beam does not saturate the 1' step. To test the ability of this scheme to accurately determine branching ratios, fine structure yields, and angular distributions including polarisation information, it has been applied to O 2 photodissociation around 130 nm with subsequent O( 3 P j ) fragment detection. [ABSTRACT FROM AUTHOR]

Detection of O( 3 P j ) atoms using one-photon resonant excitation to the 3 s 3 S 1 o state at ∼ 130 nm followed by near-threshold ionisation, i.e. 1 + 1' resonance-enhanced multi-photon ionisation, has been investigated. The aim was to achieve low ion recoil, improved sensitivity, and reliable angular momentum polarisation information, with an as simple as possible laser setup. An efficient 1 + 1' scheme has been found where the VUV light for the first step is generated by difference frequency ( 2 ω 1 − ω 2 ) VUV generation, and the ionisation step 1' uses 2 ω 2 around 289 nm. The presented scheme induces 9 m/s recoil of the O + ion using a two-dye laser system, and zero recoil should be possible by generating 302 nm radiation with a third dye laser. While this approach is much more sensitive than a previous 1 + 1' scheme using 212.6 nm for the 1' step, we found that the relatively intense radiation of the 2 ω 2 beam does not saturate the 1' step. To test the ability of this scheme to accurately determine branching ratios, fine structure yields, and angular distributions including polarisation information, it has been applied to O 2 photodissociation around 130 nm with subsequent O( 3 P j ) fragment detection. [ABSTRACT FROM AUTHOR]

The optical spectrum of diatomic OsSi has been investigated for the first time, with transitions observed in the range from 15 212 to 18 634 cm-1 (657-536 nm). Two electronic band systems have been identified along with a number of unclassified bands. Nine bands have been investigated at rotational resolution, allowing the ground state to be identified as X³Σ0+- 0+, arising from the 1σ²1π42σ²3σ²1δ² configuration. The ground X³Σ0+- state is characterized by re = 2.1207(27) Å and ΔG1/2 '' = 516.315(4) cm-1 for the most abundant isotopologue, 192Os28Si (38.63%). The A1 excited electronic state, which is thought to be primarily ³π1 in character, is characterized by T0 = 15 727.7(7) cm-1, ωe = 397.0(7) cm-1, and re = 2.236(16) Å for 192Os28Si. The B1 excited electronic state is characterized by T0 = 18 468.71 cm-1, ΔG1/2 = 324.1 cm-1, and re = 2.1987(20) Å for 192Os28Si and is thought to be primarily ¹π1 in character. These results are placed in context through a comparison to other transition metal carbides and silicides. [ABSTRACT FROM AUTHOR]

Precision measurements are performed on highly excited vibrational quantum states of molecular hydrogen. The v = 12, J = 0 - 3 rovibrational levels of H2 (X1S+ g), lying only 2000 cm-1 below the first dissociation limit, were populated by photodissociation of H2S and their level energies were accurately determined by two-photon Doppler-free spectroscopy. A comparison between the experimental results on v = 12 level energies with the best ab initio calculations shows a good agreement, where the present experimental accuracy of 3.5 × 10-3 cm-1 is more precise than theory, hence providing a gateway to further test theoretical advances in this benchmark quantum system. [ABSTRACT FROM AUTHOR]

We observe the weak S0 → S2 transitions of the T-shaped benzene dimers (Bz)2 and (Bz-d6)2 about 250 cm−1 and 220 cm−1 above their respective S0 → S 1 electronic origins using two-color resonant two-photon ionization spectroscopy. Spin-component scaled (SCS) second-order approximate coupled-cluster (CC2) calculations predict that for the tipped T-shaped geometry, the S0 → S2 electronic oscillator strength fel(S2) is ~10 times smaller than fel(S1) and the S2 state lies ~240 cm−1 above S1, in excellent agreement with experiment. The S0 → S1 (ππ *) transition is mainly localized on the “stem” benzene, with a minor stem → cap charge-transfer contribution; the S0 → S2 transition is mainly localized on the “cap” benzene. The orbitals, electronic oscillator strengths fel(S1) and fel(S2), and transition frequencies depend strongly on the tipping angle ω between the two Bz moieties. The SCS-CC2 calculated S1 and S2 excitation energies at different T-shaped, stacked-parallel and parallel-displaced stationary points of the (Bz)2 ground-state surface allow to construct approximate S1 and S2 potential energy surfaces and reveal their relation to the “excimer” states at the stacked-parallel geometry. The fel(S1) and fel(S2) transition dipole moments at the C2v -symmetric T-shape, parallel-displaced and stacked-parallel geometries are either zero or ~10 times smaller than at the tipped T-shaped geometry. This unusual property of the S0 → S1 and S0 → S2 transition-dipole moment surfaces of (Bz)2 restricts its observation by electronic spectroscopy to the tipped and tilted T-shaped geometries; the other ground-state geometries are impossible or extremely difficult to observe. The S0 → S1/S2 spectra of (Bz)2 are compared to those of imidazole ⋅ (Bz)2, which has a rigid triangular structure with a tilted (Bz)2 subunit. The S0 → S1/ S2 transitions of imidazole-(benzene)2 lie at similar energies as those of (Bz)2, confirming our assignment of the (Bz)2 S0 → S2 transition. [ABSTRACT FROM AUTHOR]

We report the vibronic and cation spectra of four rotamers of m-methoxystyrene, recorded by using the two-color resonant two-photon ionization and mass-analyzed threshold ionization techniques. The excitation energies of the S1 ← S0 electronic transition are found to be 32767, 32907, 33222, and 33281 cm-1, and the corresponding adiabatic ionization energies are 65391, 64977, 65114, and 64525 cm-1 for these isomeric species. Most of the observed active vibrations in the electronically excited S1 and cationic ground D0 states involve in-plane ring deformation and substituent-sensitive bending motions. It is found that the relative orientation of the methoxyl with respect to the vinyl group does not influence the vibrational frequencies of the ring-substituent bending modes. The two dimensional potential energy surface calculations support our experimental finding that the isomerization is restricted in the S1 and D0 states. [ABSTRACT FROM AUTHOR]

• Cascade decays of vacancies in inner-shell-photoionized iodine atom are simulated. • Spectra of cascade-produced electrons and photons are calculated. • Dependences of reemitted energy on the incident photon energy are studied. • Mean free paths of cascade electrons and photons in liquid water are estimated. • Roles of photo- and cascade electrons in local energy deposition is discussed. Cascade decays of single K to O vacancies in an isolated iodine atom are simulated by straightforward construction of the cascade decay trees. Cascade-emitted electron and photon spectra are calculated and analyzed to determine the portions of energies (a) absorbed by the iodine atom after ionization and complete cascade relaxation, (b) emitted by cascade electrons, (c) emitted by cascade photons. These quantities are calculated as functions of incident photon energy following photoionization of the iodine atom in the 0.01–100 keV energy range. Cascade electrons and photoelectrons are shown to be principal energy transmitters from an ionized iodine atom to the environment. Presented data are relevant for developing the strategies of photon activation radiation therapy when iodine is used as a radiosensitizing agent. [ABSTRACT FROM AUTHOR]

In the present paper, we study nonresonant corrections for experimental measurements of the transition frequencies in the helium atom. Having attracted more attention, such effects can make a significant contribution to experiments based on one- and two-photon atomic spectroscopy. The quantum interference effects in the measurements of n3S1 − 33D1 (n = 3, 4, 5) transition frequencies based on Doppler-free two-photon spectroscopy, are considered as a possible source of current discrepancy between the experimental and theoretical data. We demonstrate that line profile asymmetry caused by the quantum interference of fine sub-levels of the state can reach tenths of a megahertz for different experimental conditions. Thus, previously unaccounted nonresonant corrections should be taken in next-generation experimental measurements of transitions frequencies in helium. However, they could not completely eliminate the current imbalance in the study of helium spectra and the question is still open. [ABSTRACT FROM AUTHOR]