CN Band Research Articles

Symmetry‐Breaking Charge Transfer and Hydrogen Bonding: Toward Asymmetrical Photochemistry

AbstractSymmetry‐breaking charge transfer upon photoexcitation of a linear A‐π‐D‐π‐A molecule (D and A being electron donating and accepting groups) could be visualized using ultrafast time‐resolved infrared spectroscopy by monitoring the CN stretching modes on the A units. Whereas in apolar solvents, the S1 state remains symmetric and quadrupolar, symmetry breaking occurs within ca. 100 fs in polar solvents as shown by the presence of two CN bands, instead of one in apolar solvents, with a splitting that increases with polarity. In protic solvents, symmetry breaking is significantly amplified by H‐bonding interactions, which are the strongest at the CN group with the highest basicity. In strongly protic solvents, the two CN bands transform in about 20 ps into new bands with a larger splitting, and the lifetime of the S1 state is substantially reduced. This is attributed to the formation of an excited asymmetric tight H‐bond complex.

Symmetry‐Breaking Charge Transfer and Hydrogen Bonding: Toward Asymmetrical Photochemistry

Symmetry-breaking charge transfer upon photoexcitation of a linear A-π-D-π-A molecule (D and A being electron donating and accepting groups) could be visualized using ultrafast time-resolved infrared spectroscopy by monitoring the CN stretching modes on the A units. Whereas in apolar solvents, the S1 state remains symmetric and quadrupolar, symmetry breaking occurs within ca. 100 fs in polar solvents as shown by the presence of two CN bands, instead of one in apolar solvents, with a splitting that increases with polarity. In protic solvents, symmetry breaking is significantly amplified by H-bonding interactions, which are the strongest at the CN group with the highest basicity. In strongly protic solvents, the two CN bands transform in about 20 ps into new bands with a larger splitting, and the lifetime of the S1 state is substantially reduced. This is attributed to the formation of an excited asymmetric tight H-bond complex.

Detection of Copper(II) Ions Using Glycine on Hydrazine-Adsorbed Gold Nanoparticles via Raman Spectroscopy.

A facile, selective, and sensitive detection method for the Cu2+ ions in environmental and biological solutions has been newly developed by observing the unique CN stretching peaks at ~2108 cm−1 upon the dissociative adsorption of glycine (GLY) in hydrazine buffer on gold nanoparticles (AuNPs). The relative abundance of Cu species on AuNPs was identified from X-ray photoelectron spectroscopy analysis. UV-Vis spectra also indicated that the Au particles aggregated to result in the color change owing to the destabilization induced by the GLY-Cu2+ complex. The CN stretching band at ~2108 cm−1 could be observed to indicate the formation of the CN species from GLY on the hydrazine-covered AuNP surfaces. The other ions of Fe3+, Fe2+, Hg2+, Mg2+, Mn2+, Ni2+, Zn2+, Cr3+, Co2+, Cd2+, Pb2+, Ca2+, NH4+, Na+, and K+ at high concentrations of 50 µM did not produce such spectral changes. The detection limit based on the CN band for the determination of the Cu2+ ion could be estimated to be as low as 500 nM in distilled water and 1 µM in river water, respectively. We attempted to apply our method to estimate intracellular ion detection in cancer cells for more practical purposes.

Investigation of inclusion complex of HP-γ-cyclodextrin with ceftazidime

The inclusion complex of ceftazidime (CF) with hydroxypropyl-γ-cyclodextrin (HP-γ-CD) was prepared. The inclusion behavior and interactions of CF with HP-γ-CD was carried out in both the solution and the solid state by UV/vis, FT-IR, NMR and molecular docking techniques. All the obtained information demonstrated the formation of CF-CD inclusion complex. The CF-CD inclusion complex exhibited different spectroscopic features and properties from CF. The results suggested that CF-CD inclusion complex was established with 1:1 stoichiometry. It was found that a part of CF molecule, the thiazole ring with sulfur and nitrogen atoms with CO and CN bands of CF was included in the HP-γ-CD cavity. Also the solubility and stability of CF-HP-γ-CD was significantly improved and consequently the bioavailability of CF through CF-CD inclusion complex was effectively improved over free CF. Based on the enhancement of absorbance of CF in the presence of HP-γ-CD a sensitive spectroscopic method for the CF determination was developed.

NOESY-Like 2D-IR Spectroscopy Reveals Non-Gaussian Dynamics.

We have identified an unexpected signature of non-Gaussian dynamics in a conventional 2D IR measurement on a system with rapid intermolecular vibrational energy transfer. In a ternary mixture of the CO2 reduction photocatalyst, ReCl(bpy)(CO)3, NaSCN, and THF solvent, preferential association between the metal carbonyl catalyst and the NaSCN ion pairs facilitates intermolecular energy transfer on a few picoseconds time scale. Monitoring the cross peak between the highest frequency metal carbonyl band and the CN bands of NaSCN contact ion pairs, we find a striking time evolution of the cross-peak position on the detection axis. This frequency shift, which is due to spectral diffusion following intermolecular energy transfer, occurs with a time scale that is distinct from either the donor or acceptor spectral diffusion measured simultaneously. We argue that the energy transfer, a second-order Förster process, effectively increases the dimensionality of the 2D-IR spectroscopy and thus enables sensitivity to non-Gaussian dynamics.

Evidence for multiple populations in the intermediate-age cluster Lindsay 1 in the SMC

Abstract Lindsay 1 is an intermediate-age (≈8 Gyr) massive cluster in the Small Magellanic Cloud. Using VLT FORS2 spectra of 16 probable cluster members on the lower red giant branch of the cluster, we measure CN and CH band strengths (at ≃ 3883 and 4300 Å, respectively), along with carbon and nitrogen abundances and find that a sub-population of stars has significant nitrogen enrichment. A lack of spread in carbon abundances excludes evolutionary mixing as the source of this enrichment, so we conclude that this is evidence of multiple populations. Therefore, Lindsay 1 is the youngest cluster to show such variations, implying that the process triggering the onset of multiple populations must operate until at least redshift ∼1.

CARBON STARS FROM LAMOST DR2 DATA

ABSTRACT In this work, we present the new catalog of carbon stars from the LAMOST DR2 catalog. In total, 894 carbon stars are identified from multiple line indices measured from the stellar spectra. We are able to identify the carbon stars by combining the CN bands in the red end with C2 and other lines. Moreover, we also classify the carbon stars into spectral sub-types of C–H, C–R, and C–N. These sub-types show distinct features in the multi-dimensional line indices, implying that in the future they can be used to identify carbon stars from larger spectroscopic data sets. While the C–N stars are clearly separated from the others in the line index space, we find no clear separation between the C–R and C–H sub-types. The C–R and C–H stars seem to smoothly transition from one to another. This may hint that the C–R and C–H stars may not be different in their origins, instead their spectra look different because of different metallicities. Due to the relatively low spectral resolution and lower signal-to-noise ratio, the ratio of 12C/13C is not measured and thus the C–J stars are not identified.

Carbon Ablative Shock-Layer Radiation with High Surface Temperatures

Despite the prominence of carbon-based materials for use in thermal protection systems, much uncertainty remains in predicting thermochemical ablation rates at high surface temperatures. To address this issue, experiments using preheated graphite models with surface temperatures up to 3300 K were conducted in the X2 expansion tunnel at the University of Queensland. Calibrated shock-layer emission measurements in the wavelength region from 353 to 391 nm were taken to observe the effect of surface temperature on radiation from the CN violet and bands. Numerical simulations were conducted using US3D with modified Park as well as Zhluktov and Abe surface thermochemistry models. Lines of sight extracted from the flowfield data were simulated in NEQAIR to reproduce the experimental radiance profiles. It was found that the experimental CN radiance showed no significant dependence on surface temperature, whereas the numerical simulations predicted a monotonic increase with temperature for all surface models. Several potential mechanisms for these discrepancies have been identified and discussed.

Scl-1013644: a CEMP-s star in the Sculptor dwarf spheroidal galaxy

Recent studies of the Milky Way and its satellites have paid special attention to the importance of carbon-enhanced metal-poor (CEMP) stars due to their involvement in Galactic formation history and their possible connection with the chemical elements originating in the first stellar generation. In an ongoing study of red giants in the Sculptor dwarf galaxy we have discovered a star with extremely strong CN and CH molecular bands. This star, Scl-1013644, has previously been identified by Geisler et al. (2005) as a star with an enrichment in the heavy elements. Spectrum synthesis has been used to derive the carbon, nitrogen and barium abundances for Scl-1013644. Our findings are [C/Fe] = +0.8, [N/Fe] = -0.3 and [Ba/Fe] = +2.1 with the latter result consistent with the value found by Geisler et al. (2005). These results reveal Scl-1013644 as a CEMP-s star, the third such star discovered in this dwarf galaxy.

LIMITATIONS OF CN AND CH MOLECULAR BAND STRENGTHS AT HIGH METALLICITIES: A CASE STUDY IN NGC 6791

ABSTRACT We present an analysis of the CN and CH molecular band strengths in NGC 6791 from low-resolution Sloan Extension for Galactic Understanding and Exploration spectra as a means to detect chemical variations in the cluster. NGC 6791 is a heavily studied open cluster (OC) due to its unique combination of old age, high mass, and high metallicity. These characteristics place NGC 6791 between the physical properties of most globular and OCs. Recent photometric and spectroscopic studies yield contradicting results, with some claiming to detect signs of multiple populations, as in globular clusters, while others do not. We do not find large spreads in the CN and CH band strength distributions that would suggest multiple populations. By pairing spectral synthesis with the measured CN values, we conclude that the maximum [N/Fe] variation in the cluster is 0.2 dex. Additionally, we find that the saturation of the CH band at high metallicities limits its usefulness in detecting multiple populations and determining C abundances.

Differentiation of Positional Isomers of Propyl Alcohols Using Filament-Induced Fluorescence**Supported by the National Natural Science Foundation of China under Grant Nos 61427816 and 61235003, the Research Fund for the Doctoral Program of Higher Education of China under Grant No 20130061110047, and the Open Fund of the State Key Laboratory of High Field Laser Physics.

We experimentally demonstrate the recognition of positional isomers of propyl alcohol vapor through nonlinear fluorescence induced by high-intensity femtosecond laser filaments in air. By measuring characteristic fluorescence of n-propyl and isopropyl alcohol vapors produced by femtosecond filament excitation, it is found that they show identical spectra, that is, those from molecular bands of CH, C2, NH, OH and CN, while the relative intensities are different. By comparing the ratios of the CH and C2 signals, the two propyl alcohol isomers are differentiated. The different signal intensities are ascribed to different ionization potentials of the two isomer molecules, leading to different production efficiencies of fluorescing fragments.

CN and C2 vibrational spectra analysis in molecular LIBS of organic materials

With the objective of investigation of the influence of molecular structure on CN violet and C2 Swan bands system spectra, plasma emissions from different organic materials, including polycyclic aromatic hydrocarbons, aromatic carboxylic acid, aliphatic carboxylic acid, amides and polymers, have been analyzed by laser-induced breakdown spectroscopy (LIBS) technique in air. To evaluate the influence of N2 and O2 molecules concentration on the CN and C2 molecular emissions, LIB spectra of four different samples have been recorded in air (approximately 80 % N2 and 20 % O2), nitrogen, oxygen and argon atmospheres. Experimental results indicate that the main reason for the absence of C2 emission in LIB spectra of samples which do not contain C–C bonds, when measurements were taken in air, is the presence of oxygen which could potentially deplete C2 emission rather than the absence of C–C bonds in their structure. Also, comparisons between experiment and theory spectra are made using a Nelder–Mead temperature program for CN and C2 bands with the ∆ν = 0 sequences from LIB spectra of different samples in various atmospheres. Furthermore, CN and C2 vibrational temperatures in Kelvin (K) are calculated from these spectral fittings. Both CN and C2 vibrational temperatures have highest values in argon atmosphere, and increasing the oxygen concentration in ambient atmosphere decreased those in most cases.

Approach for determination of detonation performance and aluminum percentage of aluminized-based explosives by laser-induced breakdown spectroscopy.

Energetic materials containing aluminum powder are hazardous compounds, which have wide applications as propellants, explosives, and pyrotechnics. This work introduces a new method on the basis of the laser-induced breakdown spectroscopy technique in air and argon atmospheres to investigate determination of aluminum content and detonation performance of 1,3,5-trinitro-1,3,5-triazine (RDX)-based aluminized explosives. Plasma emission of aluminized RDX explosives are recorded where atomic lines of Al, C, H, N, and O, as well as molecular bands of AlO and CN are identified. The formation mechanism of AlO and CN molecular bands is affected by the aluminum percentage and oxygen content present in the composition and plasma. Relative intensity of the Al/O is used to determine detonation velocity and pressure of the RDX/Al samples. The released energy in the laser-induced plasma of aluminized RDX composition is related to the heat of explosion and percentage of aluminum.

A Comparison Between the Patterns of CN, O, and Na Inhomogeneities on the Red Giant Branch of Messier 71 Using Data from the Literature

Data drawn from the published literature are used to define the relations between the spectroscopic λ4215 CN-band strength of red giants in the globular cluster Messier 71 and both the sodium and oxygen abundances. The cluster giants with CN measurements included in this study have absolute magnitudes in the range -2 < M V < +2. The data are consistent with a moderate degree of anticorrelation between the CN-band strength and the [O/Fe] abundance, as well as a moderate correlation between CN-band strength and [Na/Fe], although there is scatter of up to 0.3–0.4 dex in both O and Na abundance among giants with CN bands of similar strength. The mean difference in [O/Fe] between CN-strong and CN-weak giants is 0.13 dex, the former group of stars having the lower average oxygen abundance. By contrast, the mean difference in [Na/Fe] between CN-strong and CN-weak giants is 0.17 dex, with the CN-strong group having the higher average sodium abundance. There is a similar range in λ4215 CN-band strengths among the red giants in Messier 71 and 47 Tucanae. Furthermore, the red giant branch stars in the two clusters follow very similar relations between CN-band strength and [Na/Fe] abundance. These two similarities are intriguing given that the two clusters differ by a factor of 30 or more in luminous mass, with 47 Tuc having a much higher degree of central mass concentration than M71. A difference can be discerned between the O-CN relations in the two clusters, such that for a given CN-band strength the CN-strong giants in 47 Tuc attain lower values of [O/Fe], a result that is consistent with previously noted differences in the O-Na relations of the two objects. A scenario is discussed in which both 47 Tuc and M71 were formed as the mergers of pre-existing CN-weak and CN-strong subclusters, the later having been formed following chemical evolution and self-enrichment of a large cloud complex that had earlier formed the CN-weak subcluster. Different dynamical merger routes may have lead in one instance to the high-mass 47 Tuc cluster, whereas M71 may have resulted from a merger that was accompanied by a large amount of star loss and stellar evaporation.

A novel approach for investigation of chemical aging in composite propellants through laser-induced breakdown spectroscopy (LIBS)

Many methods have been developed in recent years for the analysis and evaluation of energetic materials. This work introduces a novel approach for the analysis and aging of solid composite propellants by laser-induced breakdown spectroscopy (LIBS). The results of the plasma spectrum were used to investigate the behavior of the aged samples. For this purpose, CN and AlO molecular bands of different samples were compared with each other. The samples were examined under inert argon atmosphere to study LIBS signal improvement. Some absent lines such as C and C2 swan bands were detected and reduction of air impact was carried out. Line intensity ratios of samples were changed for all samples during their aging. Differential scanning calorimetry (DSC) method was used to compare them with the output of LIBS’s technique. The results of LIBS and DSC methods show a similar trend in changing mechanical and thermal properties.

Improved Measurement Performance of Inorganic Elements in Coal by Laser-Induced Breakdown Spectroscopy Coupled with Internal Standardization**supported by Open Research Fund of State Key Laboratory of Pulsed Power Laser Technology of China (No. SKL2013KF03), National Natural Science Foundation of China (Nos. 51206055, 51476061), the Fundamental Research Funds for the Central Universities of China (No. 2014ZZ0014), the New Star of Pearl River

Laser-induced breakdown spectroscopy was employed to determine the inorganic elements in coal. To improve the measurement's accuracy and precision, a new internal standardization scheme, which we named changed internal standardization, was compared with the traditional internal standardization and no internal standardization for the analysis of inorganic elements. The new internal standardization scheme used the atomic line of carbon at 247.86 nm and the molecular band of CN at 388.34 nm and C2 at 516.32 nm to normalize the lines of inorganic elements that were distributed in the same spectral channel. The performance of the utilization of the new internal standardization scheme was evaluated using a set of coal samples, including twenty calibration samples and five validation samples. The results show that the coefficients of determination R2 and the slope of calibration models coupled with changed internal standardization are better than that of the calibration models coupled with fixed internal standardization and no internal standardization. Moreover, the measurement accuracy and reproducibility of changed internal standardization for the analysis of five validation samples also yielded further improvement. The results that we obtained suggest that changed internal standardization could compensate for the matrix effects, as well as the influence of the difference in the spectral response of the light collection system.

LOW-RESOLUTION SPECTROSCOPIC STUDIES OF GLOBULAR CLUSTERS WITH MULTIPLE POPULATIONS

Recent narrow-band Ca photometry discovered two distinct red giant branch (RGB) populations in some massive globular clusters (GCs) including M22, NGC 1851, and NGC 288. In order to investigate the differences in light/heavy elements abundances between the two subpopulations, we have performed low-resolution spectroscopy for stars on the two RGBs in these GCs. We find a significant difference (more than <TEX>$4{\sigma}$</TEX>) in calcium abundance from the spectroscopic HK' index for both M22 and NGC 1851. We also find a more than <TEX>$8{\sigma}$</TEX> difference in CN band strength between the Ca-strong and Ca-weak subpopulations. For NGC 288, however, we detect the presence of a large difference only in the CN strength. The calcium abundances of the two subpopulations in this GC are identical within errors. We also find interesting differences in CN-CH relations among these GCs. While CN and CH indices are correlated in M22, they show an anti-correlation in NGC 288. However, NGC 1851 shows no difference in CH between two groups of stars having different CN strengths. The CN bimodality in these GCs could be explained by pollution from intermediate-mass asymptotic giant branch stars and/or fast-rotating massive stars. For the presence or absence of calcium bimodality and the differences in CN-CH relations, we suggest these would be best explained by how strongly type II supernovae enrichment has contributed to the chemical evolutions of these GCs.

A Comparison Between the Patterns of CN, O, and Na Inhomogeneities on the Red Giant Branch of 47 Tucanae

Data from the literature are drawn together to compare the λ4215 CN band strength of red giant stars in the globular cluster 47 Tucanae with their sodium and oxygen abundances. Most cluster giants included in this study have absolute magnitudes brighter than M V = +0.5, i.e., they are brighter than the horizontal branch. Among the majority of these cluster giants, it is possible to identify an anticorrelation between the CN band strength and the [O/Fe] abundance, along with a correlation between CN band strength and [Na/Fe], although a small number of stars seem to be exceptions to these trends. As regards the CN-weak and CN-strong populations of red giants in 47 Tuc, the former has a higher mean oxygen abundance and a lower mean sodium abundance than the later. Both populations may contain a small fraction of stars whose sodium or oxygen abundances differ by ∼0.2 dex from the mean of each population. A scenario is discussed in which 47 Tuc was the result of an early merger between a CN-poor and a CN-strong subcluster of stars that formed at different locations within the interior of a chemically evolving massive gas complex.

Synthesis and characterization of tetraacetonitrilolithiumhexafluorophosphate crystal

Tetraacetonitrilolithiumhexafluorophosphate (Li(CH3CN)4PF6) crystal is an important intermediate in the preparation of high purity lithium hexafluorophosphate electrolyte via a simple transformation method. In this study, the crystal parameters were determined by X-ray powder diffraction analysis, which showed that it belongs to the triclinic system with space group P1. FTIR spectral studies identified the characteristic absorption bands of CN and PF6− in the synthesized complex. Chemical analysis, gas chromatography, and ICP-AES results showed that the elementary ratio of Li:P:F: CH3CN in the complex is approximately: 1:1:6:4. Furthermore, the geometric optimization structure of Li(CH3CN)4PF6 was obtained using GAUSSIAN 09 program on a B3LYP/6-31+G(d, p) level. In this structure, two acetonitrile ligands bind strongly with the Li+ ion, whereas the other two are weakly-coordinated with lithium. The results of solid-state 13C-, 31P-, and 19F-NMR spectra confirmed that this configuration is reasonable.

LOW-RESOLUTION SPECTROSCOPY FOR THE GLOBULAR CLUSTERS WITH SIGNS OF SUPERNOVA ENRICHMENT: M22, NGC 1851, AND NGC 288

There is increasing evidence for the presence of multiple red giant branches (RGBs) in the color-magnitude diagrams of massive globular clusters (GCs). In order to investigate the origin of this split on the RGB, we have performed new narrow-band Ca photometry and low-resolution spectroscopy for M22, NGC 1851, and NGC 288. We find significant differences (more than 4 sigma) in calcium abundance from the spectroscopic HK' index for M22 and NGC 1851. We also find more than 8 sigma differences in CN band strength between the Ca-strong and Ca-weak subpopulations for these GCs. For NGC 288, however, a large difference is detected only in the CN strength. The calcium abundances of RGB stars in this GC are identical to within the errors. This is consistent with the conclusion from our new Ca photometry, where the RGB splits are confirmed in M22 and NGC 1851, but not in NGC 288. We also find interesting differences in CN-CH correlations among these GCs. While CN and CH are anti-correlated in NGC 288, they show positive correlation in M22. NGC 1851, however, shows no difference in CH between the two groups of stars with different CN strengths. We suggest that all of these systematic differences would be best explained by how strongly type II supernovae enrichment has contributed to the chemical evolution of these GCs.