Spectroscopic Work Research Articles

Infrared Spectra and Vapor Pressures of Crystalline C2N2, with Comparisons to Crystalline HCN

In a continuation of our work on nitriles, we have examined cyanogen (C2N2) as a crystalline solid, comparing the results to our recent work on crystalline hydrogen cyanide (HCN). A density and refractive index for C2N2 ice were measured and used to prepare solid samples from which infrared (IR) spectra, band strengths, and optical constants were measured. The vapor pressures (sublimation pressures) of both C2N2 and HCN ices were determined with a quartz-crystal microbalance at temperatures relevant to Titan's atmosphere and much lower than those in the literature. Comparisons of the newly measured low-temperature vapor pressures to values extrapolated from higher temperatures revealed differences on the order of 45 and 130%. The enthalpies of sublimation of C2N2 and HCN in the 120 K region were measured and found to be similar to those at higher temperatures. Comparisons were made to previous spectroscopic work, but hindered in the case of IR intensities by the lack of published details.

Transition probabilities of the AgS(A[formula omitted][formula omitted] X[formula omitted]) emission including spin–orbit coupling effects and evidence of a novel band system

A systematic spectroscopic work using multireference configuration interaction (MRCI) and coupled cluster (CC) calculations was performed in conjunction with large basis sets for AgS. As a result, a more accurate dissociation energy of 17,542 cm−1 is predicted for the X2Π using an analytical potential energy curve, including spin–orbit effects. The calculated energy separation Te(A)∼ 10,500 cm−1 suggests that the AgS(A2Σ+→ X2Π) band system is in near-IR. An unobserved 32Π→ X2Π band system is predicted with Einstein coefficient for spontaneous emission of the orders of 104–105 s−1 in the UV region (342 nm). The radiative lifetimes for the A2Σ+ are of the order of ∼100 microseconds. The AgS(A) state presents a possible predissociation channel caused by interactions with the quartet 14Σ− and 14Π states. The spin–orbit coupling effects are considered in this work by utilizing the Breit–Pauli operator. The present findings are good references for future spectroscopic research concerning heavy-element sulfides.

High-resolution rovibrational spectroscopy of trans-formic acid in the v1 OH stretching fundamental: Dark state coupling and evidence for charge delocalization dynamics

High-resolution infrared (IR) reduced-Doppler absorption spectra of jet-cooled gas phase trans-formic acid in the v1 OH stretching fundamental region are reported for the first time, obtained by supersonically expanding trans-formic acid/Ar mixtures through a slit jet nozzle source and rotationally cooling to Trot ≈ 10.9(5) K, with absorption signals recorded by high-resolution difference-frequency IR absorption spectroscopy. Two a/b-type rovibrational bands of comparable intensity, one ∼10-fold weaker b-type band, and one ∼6-fold weaker a-type band are observed, with vibrational band origins at 3570.493(5), 3566.793(5), 3560.032(9), and 3534.6869(2) cm−1, respectively. Based on previous Raman jet spectroscopic work by Nejad and Sibert [A. Nejad, E.L. Sibert III, The Raman jet spectrum of trans-formic acid and its deuterated isotopologs: Combining theory and experiment to extend the vibrational database, J. Chem. Phys. 154(6) (2021) 064301.], these four rovibrational bands have been assigned to v1, (v2 + v7), (v6 + 2v7 + 2v9), and 2v3, respectively. Specifically, two of the three upper dark states (2171 (a′) and 617292 (a′)) are close enough to the “bright” 11 (a′) state to facilitate strong anharmonic resonance interactions, which results in intensity mixing into the two zero-order bands that would otherwise be “dark”. Furthermore, our high-resolution spectral analysis reveals that there are local rotational crossings between these zero-order 11 and 2171 states resulting in extra lines (i.e., some upper levels in the nominally v1 band have majority zero-order 2171 state character). This motivates development of a 3 coupled state (11, 2171, and 617292) picture to aid in the spectral analysis, which is able to match all 3 observed band origins and relative band intensities, as well as indicate the necessity of multistate (> 2) coupling. Though limited by range of J and Ka levels (J' ≤ 9 and Ka' ≤ 3) populated at supersonic jet temperatures, this work offers first precision spectroscopic analysis of trans-formic acid in the v1 OH stretch region, which should aid in assignment of the more complete yet highly congested room temperature FTIR spectra [D. Hurtmans, F. Herregodts, M. Herman, J. Liévin, A. Campargue, A. Garnache, A. Kachanov, Spectroscopic and ab initio investigation of the νOH overtone excitation in trans-formic acid, J. Chem. Phys. 113(4) (2000) 1535–1545.]. Finally, and in sharp contrast to the spectral complexity in the three predominantly b-type bands, the lone a-type 2v3 rovibrational band at 3534.6869(2) cm−1 is well described by a simple, rigid asymmetric top Hamiltonian.

Assessing the spatial variability of the ~3 μm OH/H2O absorption feature in CM2 carbonaceous chondrites

AbstractH2O and OH are readily detected in hydrated minerals in CM chondrites via reflectance spectroscopy due to their characteristic vibration absorptions at infrared wavelengths. Previous spectroscopic work on bulk powdered CM chondrites has shown that spectral parameters, like the wavelength position of the “3 μm absorption feature,” vary systematically with the extent to which the samples have been aqueously altered. However, it is yet unclear how these spectral features may vary across an intact meteorite chip when measured at spatial scales smaller than that of the individual components of the meteorite. Here, we explore the spatial variability of this spectral feature and others on intact CM2 chips which, unlike powders, retain their petrologic and textural characteristics. We also model the modal mineralogy of the bulk meteorite powders and correlate this with key spectral features, demonstrating that microscope Fourier transform infrared spectroscopic mapping provides a powerful, rapid, and non‐destructive technique for assessing compositional diversity and variations in water–rock interactions in chondritic planetary materials. In all CM2 chondrites studied here, we find that variations in the position, shape, and strength of the 3 μm absorption feature reveal a single chondrite can exhibit as much spectral variation as the entire suite of CM2 chondrites. The observed variations in the position and shape of the 3 μm feature within individual CM2 chondrite chips suggest a range of alteration products (e.g., Mg‐rich to Fe‐rich phyllosilicates) are present and record sub‐mm scale variations in the amount and/or chemistry of the altering fluids. The samples having experienced the most progressive aqueous alteration show the least amount of variability in features like the 3 μm absorption band minimum position, whereas the least altered samples exhibit the most variability. We also find that the bulk spectral signatures in the least altered samples appear to be biased toward the spectral signatures of clasts versus matrix. By extension, asteroid reflectance spectra exhibiting 3 μm absorption features consistent with those measured here may be interpreted in a similar framework in which the spectrum of what may appear to be the least altered asteroids represents an average that belies the true diversity of mineralogy and chemistry of the body.

Surface enhanced electron correlation on the trivial quasi-two-dimensional bulk insulator 1T−TaS2

While the prototypical quasi-two-dimensional charge density wave system of $1T\text{\ensuremath{-}}{\mathrm{TaS}}_{2}$ has been known as a Mott insulator with a possibility of quantum spin liquid, recent band-structure calculations and spectroscopic works in parallel suggested a metallic system or a spin-singlet insulator due to the interlayer coupling. Here, we carefully reinvestigate the out-of-plane electron dispersion, which reflects the interlayer electronic coupling, with angle-resolved photoelectron spectroscopy. We identify two distinct branches for the topmost valence band, which can be unambiguously related to the surface and the bulk layers with different band gaps. Density functional theory calculations clearly indicate a trivial band insulator due to the interlayer coupling for the bulk but the surface band gap affected substantially by the electron correlation. The surface-bulk electronic dichotomy consistently incorporates most of the theoretical and spectroscopic results reported so far and has wide implications for van der Waals materials with nontrivial interlayer interactions.

Searching for biosignatures by their rotational spectrum: global fit and methyl group internal rotation features of dimethylsulphoxide up to 116 GHz

AbstractThe identification and quantification of molecules in interstellar space and atmospheres of planets in the solar systems and in exoplanets rely on spectroscopic methods and laboratory work is essential to provide the community with the spectral features needed to analyse cosmological observations. Rotational spectroscopy in particular, with its intrinsic high resolution, allows the unambiguous identification of biomolecular building blocks and biosignature gases which can be correlated with the origin of life or the identification of habitable planets. We report the extension of the measured rotational transition frequencies of dimethylsulphoxide and its 34S and 13C isotopologues in the millimetre wave range (59.6–78.4 GHz) by use of an absorption spectrometer based on the supersonic expansion technique. Hyperfine patterns related to the methyl group internal rotation were analysed in the microwave range region (6–18 GHz) with a Pulsed Jet Fourier Transform spectrometer at extremely high resolution (2 kHz) and reliable predictions up to 116 GHz are provided. The focus on sulphur-bearing molecules is motivated by the fact that sulphur is largely involved in the intra- and inter-molecular hydrogen bonds in proteins and although it is the 10th most abundant element in the known Universe, understanding its chemistry is still a matter of debate. Moreover, sulphur-bearing molecules, in particular dimethylsulphoxide, have been indicated as possible biosignature gases to be monitored in the search of habitable exoplanets.

On the planarity of benzyl cyanide

The microwave spectra of benzyl cyanide, C6H5CH2CN, were recorded using a molecular jet Fourier transform microwave spectrometer operating in the frequency range 2–26.5 GHz. Analyses of the 14N quadrupole hyperfine structures were performed simultaneously with the rotational frequencies. Rotational constants, centrifugal distortion constants, and nuclear quadrupole coupling constants χaa and χbb − χcc were all determined with very high accuracy in a fit containing 465 lines with standard deviation within the measurement accuracy. Results from quantum chemical calculations at many levels of theory employing the MP2 method indicate a non-planar heavy atom skeleton structure, where the CH2CN group is tilted up to 50° with respect to the phenyl ring. This conflicts with results from many calculations employing density functional theory methods and also with the conclusion of a previous microwave spectroscopic work (X.-Z. Liu, R.K. Bohn, S.A. Sorenson, N.S. True, J. Mol. Struct.243 (1991) 325–339), stating that the CH2CN group and the phenyl ring are in-plane. By comparing the planar defect with those of several planar molecules reported in the literature, and with extensive support from quantum chemistry, we present for the first time evidence suggesting that the heavy atom structure of benzyl cyanide is probably not planar.

2021 Census of Interstellar, Circumstellar, Extragalactic, Protoplanetary Disk, and Exoplanetary Molecules

Abstract To date, 241 individual molecular species, composed of 19 different elements, have been detected in the interstellar and circumstellar medium by astronomical observations. These molecules range in size from two atoms to 70 and have been detected across the electromagnetic spectrum from centimeter wavelengths to the ultraviolet. This census presents a summary of the first detection of each molecular species, including the observational facility, wavelength range, transitions, and enabling laboratory spectroscopic work, as well as listing tentative and disputed detections. Tables of molecules detected in interstellar ices, external galaxies, protoplanetary disks, and exoplanetary atmospheres are provided. A number of visual representations of these aggregate data are presented and briefly discussed in context.

Structure Set in Stone: Designing Rigid Linkers to Control the Efficiency of Intramolecular Singlet Fission.

Research on materials facilitating efficient singlet fission (SF) is driven by a possible reduction of thermalization losses in organic photovoltaic devices. Intramolecular SF (iSF) is in this context of special interest, as the targeted modification of either chromophores or linkers enables gradual variations of molecular properties. In this combined synthetic, spectroscopic, and computational work, we present and investigate nine novel spiro-linked azaarene dimers, which undergo efficient iSF with triplet yields up to 199%. Additional molecular braces enhance the rigidity of these tailor-made dimers (TMDs), resulting in great agreement between crystal structures and predicted optimal geometries for iSF in solution. Regardless of the employed chromophores and linkages, the dynamics of all nine TMDs are perfectly described by a unified kinetic model. Most notably, an increase in the orbital overlap of the π-systems by decreasing the twist angle between the two chromophores does not only increase the rate of formation of the correlated triplet pair but also further promotes its decorrelation. This new structure-function relationship represents a promising strategy toward TMDs with high triplet lifetimes to be utilized in optoelectronic devices.

Multifunctional Optical Device with a Continuous Tunability over 500 nm Spectral Range Using Polymerized Cholesteric Liquid Crystals.

We report that polymerization makes a robust, practically applicable multifunctional optical device with a continuous wavelength tunable over 500 nm spectral range using UV-polymerizable cholesteric liquid crystals (CLCs). It can be used as a circular polarizer generating an extremely high degree of circularly polarized light with |g| = 1.85~2.00. It can also be used for optical notch filters, bandwidth-variable (from ~28 nm to ~93 nm) bandpass filters, mirrors, and intensity-variable beam splitters. Furthermore, this CLC device shows excellent stability owing to the polymerization of CLC cells. Its performance remains constant for a long time (~2 years) after a high-temperature exposure (170 °C for 1 h) and an extremely high laser beam intensity exposure (~143 W/cm2 of CW 532 nm diode laser and ~2.98 MW/cm2 of Nd: YAG pulse laser operation for two hours, respectively). The optical properties of polymerized CLC were theoretically analyzed by Berreman’s 4 × 4 matrix method. The characteristics of this device were significantly improved by introducing an anti-reflection layer on the device. This wavelength-tunable and multifunctional device could dramatically increase optical research efficiency in various spectroscopic works. It could be applied to many instruments using visible and near-infrared wavelengths.

Molecular vibrational polariton: Its dynamics and potentials in novel chemistry and quantum technology.

Molecular vibrational polaritons, a hybridized quasiparticle formed by the strong coupling between molecular vibrational modes and photon cavity modes, have attracted tremendous attention in the chemical physics community due to their peculiar influence on chemical reactions. At the same time, the half-photon half-matter characteristics of polaritons make them suitable to possess properties from both sides and lead to new features that are useful for photonic and quantum technology applications. To eventually use polaritons for chemical and quantum applications, it is critical to understand their dynamics. Due to the intrinsic time scale of cavity modes and molecular vibrational modes in condensed phases, polaritons can experience dynamics on ultrafast time scales, e.g., relaxation from polaritons to dark modes. Thus, ultrafast vibrational spectroscopy becomes an ideal tool to investigate such dynamics. In this Perspective, we give an overview of recent ultrafast spectroscopic works by our group and others in the field. These recent works show that molecular vibrational polaritons can have distinct dynamics from its pure molecular counterparts, such as intermolecular vibrational energy transfer and hot vibrational dynamics. We then discuss some current challenges and future opportunities, such as the possible use of ultrafast vibrational dynamics, to understand cavity-modified reactions and routes to develop molecular vibrational polaritons as new room temperature quantum platforms.

Zachary Hudson

Angewandte ChemieVolume 133, Issue 37 p. 20251-20251 Introducing …Free Access Zachary Hudson Zachary Hudson First published: 29 July 2021 https://doi.org/10.1002/ange.202108999AboutSectionsPDF ToolsRequest permissionAdd to favorites ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Abstract “I chose my current career path because I loved teaching! My interest in teaching came first, and I grew to enjoy research later. … The most exciting thing about my research is that it brings together so many different fields …” Find out more about Zachary Hudson in his Introducing … Profile. Zachary Hudson The author presented on this page has published his first article as a submitting corresponding author in Angewandte Chemie: “Near-Infrared Emitting Boron Difluoride Curcuminoid-Based Polymers Exhibiting Thermally Activated Delayed Fluorescence as Biological Imaging Probes”: N. R. Paisley, S. V. Halldorson, M. V. Tran, R. M. Gupta, S. Kamal, W. R. Algar, Z. M. Hudson, Angew. Chem. Int. Ed. 2021, 60, doi.org/10.1002/anie.202103965; Angew. Chem. 2021, 133, doi.org/10.1002/ange.202103965. Position: Associate Professor, The University of British Columbia, Vancouver, BC (Canada) Homepage: hudsonlab.ca ORCID: orcid.org/0000-0003-1448-8070 Education: 2004–2008 B.Sc. Queen's University, Kingston (Canada) 2008–2012 Ph.D. with Suning Wang, Queen's University 2012–2014 Postdoctoral fellow with Ian Manners, University of Bristol (UK) 2014–2015 Postdoctoral fellow with Craig Hawker, University of California, Santa Barbara (USA) Research: Luminescent materials, organic electronics, polymer chemistry, self-assembly, spectroscopy Hobbies: Skiing, hiking, running Science is fun because it allows you to make a career out of your curiosity. The biggest challenge facing scientists is convincing our political leaders of the importance of what we do. I chose my current career path because I loved teaching! My interest in teaching came first, and I grew to enjoy research later. My first experiment was the Friedel–Crafts acylation of fluorene. I didn't know I was supposed to add a stir bar, and it exploded! The most exciting thing about my research is that it brings together so many different fields, challenging me to always be learning. My long-term goal is to inspire a generation of undergraduates to believe that a sustainable future is possible. The principal aspect of my personality is that I am a curious person—I like to tackle new challenges, and work in areas that I've never explored before. The best advice I have ever been given is that different people prefer to communicate in different ways, and that understanding those differences can make one a better communicator. The most important quality of a mentor is to know when your students need leadership, and when it's time to let them lead. My most important role model was my late Ph.D. supervisor Suning Wang, because she taught me to always put students first. I advise my students to share ideas freely with one another and collaborate to solve difficult problems. My biggest inspiration is my students’ creativity. The complexity and diversity of problems they can solve is greater than anything I could do on my own. My group has fun by spelling inappropriate phrases with periodic table magnets on the whiteboard when I am away. My favorite author is Iain M. Banks. My top three films of all time are Die Hard, Die Hard 2, and Die Hard with a Vengeance. To improve my work–life balance, I spend a lot of time on hiking trails with my golden retriever. Behind the Science References 1This work was inspired by research from Adachi and co-workers, who reported a high-performance class of near-IR TADF emitters for OLEDs in 2018. We saw this molecular design, and believed it could be adapted to unlock new applications in cellular imaging. We teamed up with Russ Algar, an expert in bioanalysis, to create fluorescent nanoparticles that could label and image human cancer cells. Understanding why some of the materials showed TADF behavior while others did not was puzzling, and took some clever theoretical and spectroscopic work from Nathan Paisley to unravel. Google Scholar Volume133, Issue37September 6, 2021Pages 20251-20251 This is the German version of Angewandte Chemie. Note for articles published since 1962: Do not cite this version alone. Take me to the International Edition version with citable page numbers, DOI, and citation export. We apologize for the inconvenience. ReferencesRelatedInformation

Hidden Isomer of Trifluoroacetylacetone Revealed by Matrix Isolation Infrared and Raman Spectroscopy.

Enol forms of trifluoroacetylacetone (TFacac) isolated in molecular and rare gas matrices were studied using infrared (IR) and Raman spectroscopy. Additionally, calculations using DFT B3LYP and M06-2X as well as MP2 methods were performed in order to investigate the possibility of coexistence of more than one stable enol form isomer of TFacac. Calculations predict that both stable enol isomers of TFacac, 1,1,1-trifluoro-4-hydroxy-3-penten-2-one (1) and 5,5,5-trifluoro-4-hydroxy-3-penten-2-one (2), could coexist, especially in matrices where the room temperature population is frozen, 1 being the most stable one. Raman and IR spectra of TFacac isolated in nitrogen (N2) and carbon monoxide (CO) matrices exhibit clear absorption bands, which cannot be attributed to this single isomer. Their relative band positions and intensity profiles match well with the theoretical calculations of 2. This allows us to confirm that in N2 and CO matrices both isomers exist in similar amounts. Careful examination of the spectra of TFacac in argon, xenon, neon, normal, and para-hydrogen (Ar, Xe, Ne, nH2, and pH2 respectively) matrices revealed that both isomers coexist in all the explored matrices, whereas 2 was not considered in the previous spectroscopic works. The amount of the second isomer (2) in the as-deposited samples depends on the host. The analysis of TFacac spectra in the different hosts and under various experimental conditions allows the vibrational characterization of both chelated isomers. The comparison with theoretical predictions is also investigated.

Mechanisms of Al3+ Dimerization in Alkaline Solutions.

The molecular speciation of aluminum (Al3+) in alkaline solutions is fundamental to its precipitation chemistry within a number of industrial applications that include ore refinement and industrial processing of Al wastes. Under these conditions, Al3+ is predominantly Al(OH)4-, while at high [Al3+] dimeric species are also known to form. To date, the mechanism of dimer formation remains unclear and is likely influenced by complex ion···ion interactions. In the present work, we investigate a suite of potential dimerization pathways and the role of ion pairing on energetics using static DFT calculations and DFT and density functional tight binding molecular dynamics. Specific cation effects imparted by the background electrolyte cations Na+, Li+, and K+ have been examined. Our simulations predict that, when the Al species are ion-paired with either cation, the formation of the oxo-bridged Al2O(OH)62- is favored with respect to the dihydroxo-bridged Al2(OH)82-, in agreement with previous spectroscopic work. The formation of both dimers first proceeds by bridging of two monomeric units via one hydroxo ligand, leading to a labile Al2(OH)82- isomer. The effect of contact ion pairing of Li+ and K+ on the dimerization energetics is distinctly more favorable than that of Na+, which may have an effect on further oligomerization.

New insights on the massive interacting binary UU Cassiopeiae

We present the results of our study of the close binary UU Cassiopeiae based on previously published multiwavelength photometric and spectroscopic data. Based on eclipse timings from the last 117 years, we find an improved orbital period of Po = 8.d519296(8). In addition, we find a long cycle of length T ∼ 270 d in the Ic-band data. There is no evidence for orbital period change over the last century, suggesting that the rate of mass loss from the system or mass exchange between the stars is small. Sporadic and rapid brightness drops of up to ΔV = 0.3 mag are detected throughout the orbital cycle, and infrared photometry clearly suggests the presence of circumstellar matter. We model the orbital light curve of 11 published datasets, fixing the mass ratio and cooler star temperature from previous spectroscopic work: q = 0.52 and Tc = 22 700 K. We find a system seen at an angle of 74° with a stellar separation of 52 R⊙, a temperature for the hotter star of Th = 30 200 K and, for the hotter and cooler stars, respectively, stellar masses of 17.4 and 9 M⊙, radii of 7.0 and 16.9 R⊙, and surface gravities log g = 3.98 and 2.94. We find an accretion disk surrounding the more massive star that has a radius of 21 R⊙ and a vertical thickness at its outer edge of 6.5 R⊙; the disk nearly occults the hotter star. Two active regions hotter than the surrounding disk are found, one located roughly in the expected position where the stream impacts the disk and the other on the opposite side of the disk. Changes are observed in parameters of the disk and spots in different datasets.

Architectures for light harvesting

Photosynthesis Conversion of light energy into chemical energy ultimately drives most biochemistry on earth. Photosynthetic organisms use diverse chemical and biological structures to harvest light in different environmental contexts. Croce and van Amerongen synthesized recent structural and spectroscopic work on photosystem complexes from oxygenic photosynthetic organisms. To best capture light, photosystems contain accessory light-harvesting complexes harboring complex networks of pigments that shuttle electronic excitations toward the core complex, which contains the reaction center. The arrangement of pigments and their connectivity, as seen in high-resolution x-ray and cryo–electron microscopy structures, inform our understanding of energy transfer rates derived from spectroscopic measurements and vice versa. The model that emerges is one of many parallel and unconnected pathways for energy transfer into the reaction center from the exterior light-harvesting complexes. Science , this issue p. [eaay2058][1] [1]: /lookup/doi/10.1126/science.aay2058

Infrared to visible upconversion luminescence of trivalent erbium tetrafluoroborate complexes

Upconverting erbium(III) complexes in N,N-dimethylformamide (DMF) were prepared via chloride ligand replacement by tetrafluoroborate, as suggested by changes in the spectral profile. Cl− removal as precipitated salts was evidenced by X-ray diffraction (XRD) analysis. The systematic spectroscopic work indicated optimal condition for complex preparation. Ions in the coordination site were controlled by adjusting the water phase, thus the amount of removed chloride salts. Maximum emission intensity, lower red-to-green ratio and narrower emission lines were achieved at molar ratios Er3+:BF4− = 1:7 and H2O:DMF = 0.23. Studies extended to downshifted luminescence of Eu3+-complex provided more evidences of effective BF4− coordination, through dependence of relative intensities between 5D0 electric dipole and magnetic dipole (5D0→7F1) transitions. Infrared spectra suggest BF4− coordination to RE.

Photoemission investigation of interaction between L‐cysteine and silver surface

In this study, the formation of Ag–S bond was systematically elucidated by thickness‐dependent ultraviolet photoelectron spectroscopy (UPS) in order to understand the L‐cysteine interaction with silver surface. A clean Ag(111) as the model system for silver surface was used, and L‐cysteine films on silver substrate were formed by vacuum evaporation. The orbital configurations at the interface was estimated including work function, secondary electron cutoff (SECO), highest occupied molecular orbital (HOMO) onset, position of an interface state, charge injection barrier, and ionization energy. A clear spectral feature was appeared in between Fermi edge and HOMO of L‐cysteine, and the feature can be attributed to the formation of Ag–S bonding. In the case of SECO, the maximum shift was 0.46 eV to the higher binding energy side at the nominal thickness of 1 Å. However, from the nominal thickness of 2 Å, SECO started to shift to the lower binding energy side, and at 16 Å, the SECO shifted to a value of around 0.4 eV to the lower binding energy side to almost cancel the initial vacuum level shift. This behavior can be attributed to weakening of the silver‐sulfur bond with increasing of L‐cysteine coverage referring to the literature. The photoelectron yield spectroscopy (PYS) was also performed as an additional spectroscopic work, which exhibited that the work function of silver once decreased and then recovered at low coverage. This behavior can also be assigned to a weakening the interaction of L‐cysteine with silver by increasing of L‐cysteine coverage.

Physico-chemical Properties of the Strong Tobacco Smoke Carcinogen NNK Diazonium Ion

We have explored the physico-chemical properties of the NNK diazonium ion to gain insight into its shape, bonding, charge distribution, and ro-vibrational features. This information is essential if the chemical reactivity and spectroscopic properties of this important intermediate are to be predicted. NNK diazonium ion is a well-known alkylating agent. Its enzymatic production, its reaction with DNA, and its role in mutagenesis/carcinogenesis have all received significant study. The ion itself, however, is relatively unstable and its direct observation has not yet been reported. Likewise, data on its shape, spectroscopic properties, bonding, and charge distribution are lacking. The species is sufficiently small such that its properties may be probed using sophisticated model chemistries. We present the first computational investigation of NNK diazonium ion deploying Kohn-Sham Density Functional Theory (B3LYP/6-311G∗∗) and Coupled Cluster theory (CCSD(T)/cc-pVDZ). We have obtained energies, geometries, electrostatic potential surfaces, molecular orbitals, and vibrational analyses for several energy-minimized structures. By providing detailed information on the geometry of and ro-vibrational motion in this ion, we hope to inform future, molecular dynamics, electronic structure, and/or spectroscopic work on this important reactive intermediate and on its interaction with DNA.

Dirac Fermion and Plasmon Dynamics in Graphene and 3D Topological Insulators

AbstractLight–matter interactions illuminate the nature of solids and provide a second look on associated carrier dynamics. In particular, graphene and 3D topological insulators (3D TI) with broadband electromagnetic excitation have revealed to host exotic dynamic interactions. Much of Dirac‐point physics arises from discrete lattice symmetries and nontrivial Z2 classification of Bloch states. In this review, ongoing spectroscopic works on graphene and 3D TI are presented, where special attention is on the far‐infrared terahertz (THz) spectroscopy that characterizes the intraband dynamics. The constant absorbance of graphene upon interband particle–hole generation exhibits nonclassical results of gapless dispersion, which can be elucidated by the relativistic Dirac equations with zero rest mass. The massless Dirac fermions on graphene and 3D TI surface exhibit distinct phenomena compared to the conventional systems. First, the transient responses after pulse excitation reveal the semimetallic states of the gapless electronic dispersion, where the Fermi energy in equilibrium determines the crossover from metallic to semiconducting states. Second, the 2D Dirac plasmon dispersion of graphene and 3D TI surface exhibits unconventional density dependence in comparison to the massive electronic systems. The novel optical phenomena in graphene and 3D TI surface can serve for advanced optoelectronic and optospintronic applications.