Vibrational Overtone Research Articles

Assessment of plum quality changes during postharvest storage using multispectral NIR technique

Plums are perishable fruit, and agriculture demands rapid nondestructive methods to be able to make decision on the storability and optimal postharvest technology. This study aimed to apply a multispectral technique utilizing selected NIR wavelengths to assess the quality of two plum cultivars popular on the Hungarian market. Samples of ‘Stanley’ and ‘Elena’ were stored at 1 °C, 5 °C, 10 °C and 15 °C for up to 24 days. The five bands at 906, 1060, 1336, 1454, and 1680 nm were selected based on the standard deviation values of the normalized spectra. These wavelengths are associated with vibrational overtones and combinations of C-H and O-H bonds. ANOVA confirmed the sensitive response of selected wavelengths to storage conditions, while the correlation analysis found significant relationship among absorbance readings, weight loss (WL) and soluble solids content (SSC). The SVM models achieved better performance in predicting WL and SSC in terms of R2, RMSEP, and RPD compared to PLSR. The validation revealed that SSC can be predicted using single SVM model for both cultivars with R2 = 0.984 and RMSEP = 0.196%, while WL reached R2 = 0.853 and RMSEP = 1.188%. Results suggest that prediction of WL requires individual model for each cultivar while prediction of SSC might work with one model for these cultivars.

Surface Vibration‐Mediated and Multiphonon Relaxation‐Assisted Antithermal‐Quenching Shortwave Infrared Emission in Ho‐Based Double Perovskite With Long Lifetime

AbstractThermal quenching generally predominates in Er3+ 1540 nm luminescence quenching at elevated temperatures, due to intensified lattice vibration and efficient overtone vibrational relaxation by O─H stretch. This issue impedes practical device applications of shortwave infrared Er‐doped phosphors. Herein, with the mediation of surface vibrational phonons, anti‐thermal quenching of Er3+ 1540 nm emission is reported in (220)‐dominated Er3+‐doped Cs2NaHoCl6 double perovskite. The downshifting emissions can be boosted with rising temperatures from 303 to 543 K, reaching 225%@483 K of the initial intensity at 303 K, accompanied with a long lifetime of 33.02 ms at 483 K. By combining temperature‐dependent in situ Raman and Fourier transform infrared spectroscopies with the excited‐state dynamics results, the coordination role of water molecules is verified, serving as promoters instead of quenchers on the (220) facet at high temperatures. Furthermore, efficient energy transfer from Ho3+ to Er3+ enables intense 1540 nm emission with a photoluminescence quantum yield of 78.1% under 450 nm excitation. Finally, a compact thermally stable phosphor‐converted light‐emitting diode (LED) is designed as a narrowband shortwave infrared light source with a blue LED chip. This work pushes the improved understanding of achieving thermal‐enhanced Er3+ luminescence for potential broad applications.

Bond lengths and band strengths of non-equivalent C-H bonds of 2-methyl-1,3-butadiene using density functional theory, Fourier transform IR, and cavity ringdown techniques

The C-H fundamental and overtone spectra (Δυ = 1- 4) of non-equivalent C-H bonds of isoprene (CH2=C(CH3)-CH=CH2) have been obtained using a Fourier transform infrared spectrometer. The C-H vibrational overtone spectra (Δυ = 5, 6) have been recorded using phase shift (PS) and exponential decay cavity ring down (CRD) techniques, respectively at 293 K. Theoretical density functional theory (DFT) calculations of bond lengths, harmonic, and anharmonic frequencies of isoprene and partially deuterated isoprene molecules, as well as computer deconvolution of the bands are used to identify transitions corresponding to non-equivalent C-H bonds. Harmonic frequencies ωe and anharmonicities ωexe are reported for theC-H (a) in plane and C-H (b) out of plane bonds of the methyl group, the single olefinic nonterminal C-H (o), and the four olefinic terminal C-H bonds that are defined in two groups as C-H (cis) and C-H (trans). From the Δυ = 6 peak wavenumbers, correlation functions are used to calculate C-H bond lengths, isolated frequencies, and dissociation energies. Band strengths, oscillator strengths, and transition moments are obtained experimentally for all transitions. The significance of the assigned vibrational transitions and integrated intensities of isoprene for research on Earth's atmosphere and as a potential indicator of life in exoplanets with oxygen-deprived atmospheres is examined.

Insight into deposition duration-varied crystallinity, optical parameters, morphology and electrical properties of solution-processed nanostructured CdSSe thin films

Nanostructured cadmium sulpho selenide (CdSSe) films have been grown onto glass substrates for different deposition durations via a facile solution-based method known as chemical bath deposition (CBD). XRD studies revealed that the crystallites in the films possessed hexagonal (wurtzite) structures with predominant orientation along the (002) plane. The crystallite size increased from ∼5.95 nm to ∼16.69 nm with the increase in deposition duration from 1 h to 4 h. The absorbance, transmittance and reflectance measurements were carried out. A transparency of ∼(50–80) % was obtained for the films. The direct optical energy band gap was found to decrease from 1.982 eV to 1.952 eV with the increment of deposition duration from 1 h to 4 h. SEM micrographs of the films revealed the presence of nano spherical-shaped grains with an average size ranging from ∼305 nm to ∼612 nm. HRTEM images illustrated the presence of compact nano-spherical grains and nano-crystallites distributed in random orientations. Raman spectroscopy divulged the presence of CdSe and CdS vibrational Raman modes and overtones in the films. PL spectra revealed a prominent red emission band along with weak luminescent bands in the yellow-red emission region. The presence of Cd–Se and Cd–S bonds in the films was validated using FTIR analysis. Electrical investigation revealed the linear current‒voltage relationship for the films with the rise in conductivity with deposition duration. Hence, deposition duration stands out as a vital parameter for modulating the properties of CdSSe thin films for use in photovoltaic devices and optoelectronics.

A Full‐Scale Analysis of Absorption Edges in Dye‐Doped Nonlinear Optical Polymers

AbstractA full‐scale analysis of the absorption edges by modified Tauc‐Lorentz models is essential in determining the optical bandgap and Urbach energy of semiconductors, transparent conductors, ionic compounds, and dielectric materials. This technique has not yet been applied to analyzing organic nonlinear optical (NLO) materials. This problem is tackled by preparing high‐quality films of guest–host NLO polymers with a wide thickness range from sub‐micron to 200 microns, allowing accurate measurement of full‐spectral absorption coefficients of NLO materials over four orders of magnitude by the UV‐VIS‐NIR spectroscopy. The Tauc model and a new Monolog–Lorentz model are used to study the optical absorption edge of guest‐host NLO polymers containing various push‐pull chromophores and the dependence of optical bandgap and Urbach edge on the structure and composition of materials is analyzed. The results reveal the critical transition of the Urbach exponential tail to a low energy tail that overlaps with vibrational overtones of materials at the telecom wavelengths. Determining the fundamental absorption region of organic NLO films in this study provides quantitative insight into the research to harness the resonance‐enhanced nonlinear coefficients of materials by operating at the wavelengths near the band edge with the control of optical loss.

Overtone Transition 2ν1 of HCO+ and HOC+: Origin, Radiative Lifetime, Collisional Quenching.

We present spectra of the first overtone vibration transition of C-H/ O-H stretch (2ν1) in HCO+ and HOC+, recorded using a laser induced reaction action scheme inside a cryogenic 22 pole radio frequency trap. Band origins have been located at 6078.68411(19) and 6360.17630(26) cm-1, respectively. We introduce a technique based on mass selective ejection from the ion trap for recording background free action spectra. Varying the number density of the neutral action scheme reactant (CO2 and Ar, respectively) and collisional partner reactant inside the ion trap, permitted us to estimate the radiative lifetime of the state to be 1.53(34) and 1.22(34) ms, respectively, and the collisional quenching rates of HCO+(2ν1) with He, H2, and N2.

Optical properties of nanocomposites based on polypropylene modified by nanoparticles of oxide compounds

The optical properties in UV, visible and near IR spectral regions for nanocomposites based on polypropylene modified by nanoparticles of oxide compounds ZrO2, Al2O3, SiO2, MgO, TiO2, ZnO were studied. A shift of the main optical absorption edge to the short-wave region upon modification by dielectric nanoparticles (MgO, ZrO2, and Al2O3) was established. The absorption edge shifts to the long-wave region upon the introduction of semiconductor nanoparticles (ZnO, TiO2) and amorphous SiO2 particles. In all spectra, the absorption bands at 1200, 1400, and 1720 nm characterized by overtone vibrations of CH, CH2, and CH3 molecular groups were recorded. OH groups make a certain contribution to the bands at 1400 and 1720 nm. The dependence of the intensity of these absorption bands on the type and concentration of nanoparticles used in the modification of polypropylene was analyzed. X-ray diffraction analysis of the studied nanocomposites was carried out, the formation of β-PP was registered upon modification by Al2O3 nanoparticles. Photoluminescence spectra of nanocomposites were studied. It was found that the introduction of nanoparticles (except SiO2) does not lead to the formation of new luminescence bands in PP.

Prospect for precision quantum logic spectroscopy of vibrational overtone transitions in molecular oxygen ions

Precision spectroscopy has been the driving force for progress of our physical understanding and still is a promising tool for the investigation of new physics. Molecules offer transitions which allow tests that are not possible in atomic systems. However, usually precision spectroscopy of molecules is challenging due to the lack of cycling transitions for state preparation and state detection. For molecular ions, this obstacle can be overcome by quantum logic spectroscopy, where dissipation for state preparation and detection is provided by a co-trapped atomic ion exploiting the shared eigenstates of motion. Here, we propose a full quantum logic spectroscopy scheme for molecular oxygen ions and theoretically investigate the feasibility of quantum logic-assisted state detection and preparation. Furthermore, we provide coupling rates for a direct single-photon quadrupole excitation of a vibrational overtone transition that can serve as a sensitive reference for tests of a possible variation of the proton-to-electron mass ratio.

Determination of the pressure and composition of wet gas fluid inclusions: An in situ Raman spectroscopic approach

Carbonaceous fluid within mineral-hosted inclusions provides important information for carbon cycle in deep Earth. In addition to CH4 and CO2, heavy hydrocarbons (e.g., C2H6 and C3H8) are frequently observed in carbonaceous fluid inclusions (i.e, wet gas inclusions with C1/∑Ci < 0.95). However, determination of the composition of such complex volatiles is difficult based on traditional microthermometric measurements. Here we carried out experimental calibrations on Raman spectroscopic measurements of the pressure (P) and composition of the CH4 ± C2H6 ± C3H8 ± H2S system at room temperature and 0.1–130 MPa. We confirmed that the C–H symmetric stretching vibration band of CH4 [ν1(CH4), ∼2917 cm−1] shifted to lower wavenumber with rising pressure, thus the P-ν1(CH4) relationship could be applied to calculate the pressure of wet gas. It should be noted that the presence of C2+ and/or H2S will shift the [ν1(CH4)] to lower wavenumber at constant pressure (with the order of C3H8 ≥ H2S > C2H6). Obviously, the P-ν1(CH4) relationship derived from pure CH4 system could not be simply applied to wet gas inclusion, otherwise the pressure would be overestimated. To avoid the overlap of the C–H vibrations of CH4, C2H6 and C3H8, the peak areas and peak heights of the overtone vibration of CH4 [2ν4(CH4), ∼2580 cm−1], C–C symmetric stretching vibrations of C2H6 [ν3(C2H6), ∼995 cm−1] and C3H8 [ν8(C3H8), ∼868 cm−1], and S–H symmetric stretching vibration of H2S [ν1(H2S), ∼2612 cm−1] were fitted using Gaussian + Lorentz functions. The obtained peak areas and peak heights were then used to calculate the Raman quantification factors (F factor and G factor, respectively) of C2H6, C3H8 and H2S relative to CH4, respectively. Both the F factor and G factor increased with rising pressure, whereas the FC2H6, FC3H8 and GH2S kept nearly constant at ∼5.69, 6.39 and 153.8, respectively in high pressure gas mixtures (e.g., >30 MPa). Therefore, for inclusions with higher internal pressure, the molar ratio of CH4, C2H6, C3H8 and H2S could be determined by the aforementioned F and G factors. This method was applied to the calcite-hosted single-phase gas inclusions in the Upper Permian Changxing Formation carbonate reservoir from the eastern Sichuan Basin (South China). Our results indicated that the trapping pressure would be obviously overestimated if the presence of heavy hydrocarbons was not taken into account.

Vibrational Anharmonicity and Energy Relaxation in Nanoscale Acoustic Resonators.

The fundamental and n = 3 overtones of Au nanoplate thickness vibrations have been studied by transient absorption microscopy. The frequencies of the n = 3 overtone are less than 3× the frequency of the fundamental. This anharmonicity is explained through a continuum mechanics model that includes organic layers on top of the nanoplate and between the nanoplate and the glass substrate. In this model, anharmonicity arises from coupling between the vibrations of the nanoplate and the organic layers, which creates avoided crossings that reduce the overtone frequencies compared to the fundamental. Comparison of the experimental and calculated quality factors shows that coupling occurs to the top organic layer. Good agreement between the measured and calculated quality factors is obtained by introducing internal damping for the nanoplate. These results show that engineering layers of soft material around metal nanostructures can be used to control the vibrational lifetimes.

Phase shift cavity ring down and FT-NIR spectra of C[sbnd]H vibrational transitions and band strengths of ethyl acetate

The vibrational overtone spectra (Δυ = 5, 6) of CH transitions of ethyl acetate (CH3COO–CH2CH3) have been obtained using the phase shift cavity ring down (PS-CRD) technique at 295 K. The CH stretch fundamental and overtone transitions (Δυ = 1- 4) have been obtained using a Fourier transform infrared and near infrared spectrophotometer. Local mode frequencies ωe and anharmonicities ωexe are reported for the CH (ip) (in plane), CH (op) (out of plane) bonds of the methyl group attached to the carbonyl (CO) side and for the methyl CH3 (primary) and methylene CH2 (secondary) CH bonds of the ethyl group bonded to the O atom. The study includes computer deconvolution of the total band at each level and a density functional theory (DFT) calculation of deuterated analogues of ethyl acetate to help with the assignment of all the non-equivalent CH bonds in the molecule. From the assigned Δυ = 6 peak wavenumber, isolated frequencies and CH bond lengths are obtained for the different CH bonds. Band strengths, oscillator strengths, and transition moments were obtained experimentally for all transitions. The importance of the assigned vibrational transitions and integrated intensities for future studies of laser and atmospheric vibrational overtone photochemistry is discussed.

Broad Dual Emission by Codoping Cr3+ (d→d) and Bi3+ (s→p) in Cs2 Ag0.6 Na0.4 InCl6 Double Perovskite.

A phosphor emitting both white light and broad near-infrared (NIR) radiation can simultaneously provide visual inspection and early signs of rotting of food products. The broad NIR emission is absorbed by the vibrational overtones of water molecules present in food items, providing the non-invasive image contrast to assess the food freshness. Here we design a phosphor, namely, Cr3+ -Bi3+ -codoped Cs2 Ag0.6 Na0.4 InCl6 , that simultaneously emit warm white light and broad NIR (1000 nm) radiation with quantum yield 27 %. This dual emitter is designed by combining the features of s2 -electron (Bi3+ ) and d3 -electron (Cr3+ ) doping in a weak crystal field of the halide perovskite host. excitation of Bi3+ , using a commercial 370 nm ultraviolet light-emitting-diodes (UV-LED), yields both the emissions. A fraction of the excited Bi3+ dopants emit the warm white light, and the other fraction transfers its energy non-radiatively to Cr3+ . Then the Cr3+ de-excites emitting broad NIR emission. Temperature dependent (6.4-300 K) photoluminescence in combination with Tanabe-Sugano diagram show that the Cr3+ experiences a weak crystal field ( =2.2), yielding the NIR emission. As a proof of concept, we fabricated a panel containing 122 phosphor-converted LEDs, demonstrating its capability to inspect food products.

Broad Dual Emission by Codoping Cr3+ (d→d) and Bi3+ (s→p) in Cs2Ag0.6Na0.4InCl6 Double Perovskite

AbstractA phosphor emitting both white light and broad near‐infrared (NIR) radiation can simultaneously provide visual inspection and early signs of rotting of food products. The broad NIR emission is absorbed by the vibrational overtones of water molecules present in food items, providing the non‐invasive image contrast to assess the food freshness. Here we design a phosphor, namely, Cr3+‐Bi3+‐codoped Cs2Ag0.6Na0.4InCl6, that simultaneously emit warm white light and broad NIR (1000 nm) radiation with quantum yield 27 %. This dual emitter is designed by combining the features of s2‐electron (Bi3+) and d3‐electron (Cr3+) doping in a weak crystal field of the halide perovskite host. excitation of Bi3+, using a commercial 370 nm ultraviolet light‐emitting‐diodes (UV‐LED), yields both the emissions. A fraction of the excited Bi3+ dopants emit the warm white light, and the other fraction transfers its energy non‐radiatively to Cr3+. Then the Cr3+ de‐excites emitting broad NIR emission. Temperature dependent (6.4–300 K) photoluminescence in combination with Tanabe‐Sugano diagram show that the Cr3+ experiences a weak crystal field ( =2.2), yielding the NIR emission. As a proof of concept, we fabricated a panel containing 122 phosphor‐converted LEDs, demonstrating its capability to inspect food products.

Vibrationally Hot Reactants in a Plasmon-Assisted Chemical Reaction.

Recent studies on plasmon-assisted chemical reactions postulate that the hot electrons of plasmon-excited nanostructures may induce a non-thermal vibrational activation of metal-bound reactants. However, the postulate has not been fully validated at the level of molecular quantum states. We directly and quantitatively prove that such activation occurs on plasmon-excited nanostructures: The anti-Stokes Raman spectra of reactants undergoing a plasmon-assisted reaction reveal that a particular vibrational mode of the reactant is selectively excited, such that the reactants possess >10 times more energy in the mode than is expected from the fully thermalized molecules at the given local temperature. Furthermore, a significant portion (∼20%) of the excited reactant is in vibrational overtone states with energies exceeding 0.5 eV. Such mode-selective multi-quantum excitation could be fully modeled by the resonant electron-molecule scattering theory. Such observations suggest that the vibrationally hot reactants are created by non-thermal hot electrons, not by thermally heated electrons or phonons of metals. The result validates the mechanism of plasmon-assisted chemical reactions and further offers a new method to explore the vibrational reaction control on metal surfaces.

Increasing the Fluorescence Quantum Yield and Lifetime of the Flavin Chromophore by Rational Design

AbstractA previous quantum chemical study (M. Bracker et al., Phys. Chem. Chem. Phys. 2019, 21, 9912–9923) on the excited state properties of fluorinated derivatives of the flavin chromophore promised an increased fluorescence performance of the derivative 7,8‐difluoro‐10‐methyl‐isoalloxazine (7,8‐dF‐MIA). Here, we describe the synthesis of 7,8‐dF‐MIA, its ribityl derivative, and for reason of comparison 9‐F‐MIA. The compounds dissolved in water (H2O and D2O) were characterized by steady state, time resolved, and fluorescence correlation spectroscopy. The experiments confirm the increase of the fluorescence quantum yield of 7,8‐dF‐MIA (0.42 in H2O) compared to MIA (0.22) predicted by quantum chemistry. The anticipated reduction of the fluorescence quantum yield for 9‐F‐MIA is also confirmed experimentally. The quantum chemical computations as well as the spectroscopic observations attribute the increased fluorescence quantum yield of 7,8‐dF‐MIA predominantly to a decrease of the rate constant of intersystem crossing. Switching from H2O to D2O as a solvent is shown to increase fluorescence quantum yields (0.53 for 7,8‐dF‐MIA) and lifetimes of all fluorinated MIA derivatives. This can be attributed to a Förster type energy transfer from the excited chromophore to vibrational overtones of water and further water‐mediated deactivation processes.

Absorption cross-sections for the 5th and 6th vibrational overtones in a series of short chained alcohols using incoherent broadband cavity enhanced-absorption spectroscopy (IBBCEAS)

Absorption cross-sections for the 5th (6 ← 0) and 6th (7 ← 0) OH overtones for gas-phase methanol, ethanol, and isopropanol were measured using a slow flow cell and Incoherent Broadband Cavity-Enhanced Absorption Spectroscopy (IBBCEAS). Measurements were performed in two wavelength regions, 447–457 nm, and 508–518 nm, using two different instruments. The experimental results are consistent with previous computational predictions of the excitation energies for these transitions. Treating the OH stretch as a local mode allowed for calculation of the fundamental vibrational frequency (ωe), anharmonicity constant (ωexe), and the vertical dissociation energy (VDE) for each alcohol studied. The fundamental vibrational frequency is 3848 ± 18 cm−1, 3807 ± 55 cm−1, and 3813 ± 63 cm−1 for methanol, ethanol, and isopropanol, respectively. The anharmonicity constant was measured to be 84.8 ± 2.1 cm−1, 80.2 ± 5.9 cm−1, and 84.4 ± 6.8 cm−1 for methanol, ethanol, and isopropanol, respectively. The OH vertical dissociation energy was measured to be 499.4 ± 18.4 kJ/mol, 518.0 ± 56.7 kJ/mol, and 492.7 ± 59.9 kJ/mol. The spectroscopically measured values are compared to thermodynamically measured OH bond dissociation energies. The observed differences in previous measurements of the bond dissociation energies compared to the values reported herein can be explained due to the difference between vertical dissociation energies and bond dissociation energies. If the OH overtone stretching mode is excited in methanol to either the 5th or 6th overtone, the bimolecular reaction between methanol and O2 becomes thermodynamically feasible and could contribute to formation of methoxy and HO2 radical under the proper combination of pressure and temperature.

A theoretical study of propynal under interstellar conditions and beyond, covering low-frequency infrared spectra, spectroscopic constants, and hot bands

ABSTRACTFrom an astrochemical point of view, propynal is a complex organic molecule. Moreover, it is a potential candidate for the formation of prebiotic propanal and propenal. Therefore, this molecule is of particular interest for astrochemical investigations. As it has been detected in the interstellar medium, it is of high relevance in this field of research. Although experimental data are available for the vibrational fundamental bands and rotational constants, experimental data for vibrational overtones and combination bands are scarce and fairly old. Additionally, high-level ab initio calculations are also not reported. In this work, we provide accurate quantum chemical calculations as well as a detailed analysis of vibrational and rovibrational properties for this molecule. The low-frequency spectrum up to $350\, \,\,\text{cm}^{-1}$ has been studied for temperatures between 10 and $300\, \text{K}$. For the same temperature range, partition functions are provided. Furthermore, the impact of hot bands up to room temperature has been investigated. A comparison of our results with experimental data is provided for the rotational constants, geometrical parameters, and a rovibrational spectrum. The underlying potential energy surface within these calculations is based on explicitly correlated coupled-cluster theory and includes up to four-mode coupling terms within an n-mode expansion. The vibrational and rovibrational calculations rely on vibrational and rovibrational configuration interaction theories, respectively.

One-color resonance enhanced two-photon ionization spectroscopy of phenylacetonitrile and its Franck-Condon simulation

Phenylacetonitrile (PAN) is widely used in the synthesis of medicines, pesticides, dyes, optoelectronic materials and quinoline derivatives, and has attracted much attention in related fields. In this paper, we report the one-color resonance enhanced two-photon ionization spectra of PAN obtained with ultrasonic molecular beam technique for the first time. The band origin of the S&lt;sub&gt;1&lt;/sub&gt; ← S&lt;sub&gt;0&lt;/sub&gt; electronic transition is determined to be (37646 ± 2) cm&lt;sup&gt;–1&lt;/sup&gt;. Density functional theory B3LYP/6-311G++(d, p) and B3LYP/aug-cc-pvtz are used to calculate the structures, energy and vibrational frequencies of the molecule. Based on these calculations Franck-Condon spectral simulations are performed. The measured vibrational frequencies are analyzed in detail. Combined with theoretical calculation, the spectral assignments are given as accurately as possible. Theoretical and experimental results are in good agreement with each other, and show that the spectrum in the low frequency region has a great signal-noise ratio and resolution, while in the high frequency region the spectrum shows opposite characteristics, revealing that the high background in high frequency region originates from dense and weak overtone and combined vibrations. Many spectral bands are found, and most of them may be assigned to the in-plane ring deformation, and theoretical calculations suggest that this is related to the expansion of the aromatic ring during the transition.

Absorption cross sections and local mode analysis for neopentane

Spectra of neopentane, 2,2-dimethylpropane, C(CH3)4, were recorded in the 1200–1650 cm-1 region by high resolution Fourier transform spectroscopy at the Canadian Light Source (CLS) and converted to absorption cross sections. Samples were at 203, 233, 266 and 294 K with 0, 10, 30 and 100 Torr of nitrogen broadening gas. The previously published cross sections in the CH stretching region (2550–3350 cm−1) [JQSRT 251, 107034 (2020)] were recalibrated and checked with two additional spectra recorded at Old Dominion University in the 1000–5000 cm−1 region. Local mode calculations for the CH stretching modes were carried out, and interactions with the overtones of the CH2 scissor vibrations were included to obtain agreement with experiment.

Electron-phonon coupling and vibrational properties of size-selected linear carbon chains by resonance Raman scattering

UV resonance Raman spectroscopy of size-selected linear sp-carbon chains unveils vibrational overtones and combinations up to the fifth order. Thanks to the tunability of the synchrotron source, we excited each H-terminated polyyne (HCnH with n = 8,10,12) to the maxima of its vibronic absorption spectrum allowing us to precisely determine the electronic and vibrational structure of the ground and excited states for the main observed vibrational mode. Selected transitions are shown to enhance specific overtone orders in the Raman spectrum in a specific way that can be explained by a simple analytical model based on Albrecht’s theory of resonance Raman scattering. The determined Huang–Rhys factors indicate a strong and size-dependent electron-phonon coupling increasing with the sp-carbon chain length.