Weak Overtone Research Articles

Pure rotational and rovibrational spectroscopy of cyclopropylamine in the far-infrared region: -NH2 torsion.

The pure rotational and rovibrational spectra of the ν27 -NH2 torsion of cyclopropylamine (CPA) in the far-infrared region were measured with a high-resolution Fourier transform infrared coupled to a synchrotron. The complex spectra reflect the presence of both trans and gauche conformers. Analysis of the pure rotational spectra (34-64cm-1) yielded accurate rotational and centrifugal distortion constants of the ground and first two torsional excited states of trans-CPA. The fundamental, hot bands and weak overtones were identified and assigned in the 200-550cm-1 range. Global analysis of over 19 000 transitions provides accurate energy levels of the torsional polyads up to vT = 3. The torsional levels and their rotational constants were in agreement with the theoretical results from quasiadiabatic channel reaction path Hamiltonian (RPH) calculations, emphasizing the need for molecular-specific theoretical treatments for large amplitude motions. Tunneling components of the torsional fundamental of gauche-CPA were assigned based on the RPH results and symmetry considerations, differing from previous experimental and theoretical work. This comprehensive spectroscopic characterization of CPA is crucial for its potential detection in the interstellar medium as a precursor to complex prebiotic molecules, providing essential data for future astronomical searches and advancing our understanding of nitrogen-containing organic molecules in space.

Ultraviolet Resonance Raman Spectra of Serum Albumins.

The ultraviolet resonance Raman (UVRR) spectra of the two proteins bovine serum albumin (BSA) and human serum albumin (HSA) in an aqueous solution are compared with the aim to distinguish between them based on their very similar amino acid composition and structure and to obtain signals from tryptophan that has only very few residues. Comparison of the protein spectra with solutions of tryptophan, tyrosine, and phenylalanine in comparative ratios as in the two proteins shows that at an excitation wavelength of 220 nm, the spectra are dominated by the strong resonant contribution from these three amino acids. While the strong enhancement of two and one single tryptophan residue in BSA and HSA, respectively, results in pronounced bands assigned to fundamental vibrations of tryptophan, its weaker overtones and combination bands do not play a major role in the spectral range above 1800 cm-1. There, the protein spectra clearly reveal the signals of overtones and combination bands of phenylalanine and tyrosine. Assignments of spectral features in the range of Raman shifts from 3800 to 5100 cm-1 to combinations comprising fundamentals and overtones of tyrosine were supported by spectra of amino acid mixtures that contain deuterated tyrosine. The information in the high-frequency region of the UVRR spectra could provide information that is complementary to near-infrared absorption spectroscopy of the proteins.

Measurement and calculation of CO (7-0) overtone line intensities.

Intensities of 14 lines in the sixth overtone (7-0) band of carbon monoxide (12C16O) are measured in the visible range between 14300 and 14500 cm-1 using a frequency-stabilized cavity ring-down spectrometer. This is the first observation of such a high and weak overtone spectrum of the CO molecule. A theoretical model is constructed and tested based on the use of a high accuracy abinitio dipole moment curve and a semi-empirical potential energy curve. Accurate studies of high overtone transitions provide a challenge to both experiment and theory as the lines are very weak: below 2 × 10-29cmmolecule-1 at 296K. Agreement between theory and experiment within the experimental uncertainty of a few percent is obtained. However, this agreement is only achieved after issues with the stability of the Davidson correction to the multi-reference configuration interaction calculations are addressed.

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<sub>1</sub> ← S<sub>0</sub> electronic transition is determined to be (37646 ± 2) cm<sup>–1</sup>. 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.

Second-Order Raman Scattering in Ferroelectric Ceramic Solid Solutions LiNbxTa1−xO3

In the second-order Raman spectra of ceramic solid solutions, LiNbxTa1−xO3 weak overtone bands of fully symmetric fundamental polar excitations were observed for the first time. The frequencies of the two bands exceeded the value of the overtone frequency corresponding to the fully symmetrical vibration 4A1(z). The possibility of the existence of phonon bound states of the antipolar type in the vibrational spectrum of LiNbxTa1−xO3 ceramics is predicted.

A Fusion of Feature-Oriented Principal Components of Multispectral Data to Map Granite Exposures of Pakistan

Despite low spatial resolutions, thermal infrared bands (TIRs) are generally more suitable for mineral mapping due to fundamental tones and high penetration in vegetated areas compared to shortwave infrared (SWIR) bands. However, the weak overtone combinations of SWIR bands for minerals can be compensated by fusing SWIR-bearing data (Sentinel-2 and Landsat-8) with other multispectral data containing fundamental tones from TIR bands. In this paper, marble in a granitic complex in Mardan District (Khyber Pakhtunkhwa) in Pakistan is discriminated by fusing feature-oriented principal component selection (FPCS) obtained from the ASTER, Landsat-8 Operational Land Imager (OLI), Thermal Infrared Sensor (TIRS) and Sentinel-2 MSI data. Cloud computing from Google Earth Engine (GEE) was used to apply FPCS before and after the decorrelation stretching of Landsat-8, ASTER, and Sentinel-2 MSI data containing five (5) bands in the Landsat-8 OLI and TIRS and six (6) bands each in the ASTER and Sentinel-2 MSI datasets, resulting in 34 components (i.e., 2 × 17 components). A weighted linear combination of selected three components was used to map granite and marble. The samples collected during field visits and petrographic analysis confirmed the remote sensing results by revealing the region’s precise contact and extent of marble and granite rock types. The experimental results reflected the theoretical advantages of the proposed approach compared with the conventional stacking of band data for PCA-based fusion. The proposed methodology was also applied to delineate granite deposits in Karoonjhar Mountains, Nagarparker (Sindh province) and the Kotah Dome, Malakand (Khyber Pakhtunkhwa Province) in Pakistan. The paper presents a cost-effective methodology by the fusion of FPCS components for granite/marble mapping during mineral resource estimation. The importance of SWIR-bearing components in fusion represents minor minerals present in granite that could be used to model the engineering properties of the rock mass.

Controls on surface wave overtone interference

SUMMARYMeasurements of fundamental-mode (FM) surface waves along the minor arc are impacted by overtone interference. This interference is primarily due to major-arc overtones for Rayleigh waves and minor-arc overtones for Love waves. In both cases, interference contaminates measurements of phase and amplitude and can introduce bias in seismic images. Here, we use synthetic seismograms computed via normal mode summation to probe how interference can vary as a function of the surface wave group velocities, source mechanism and depth, which control the relative excitation of the FM and overtones, and period. By comparing seismograms that include all overtones to those that include only the FM, we can quantify the interference, i.e., how the presence of the overtones perturbs the FM phase and amplitude. We compare the strength of this interference to calculations of excitation of the overtones and FM. We show that these calculations explain well the varying strength of interference for different source mechanisms and depths. Notably, these calculations illuminate source depths where Love wave overtone excitation is quite low and therefore interference is unusually weak, and depths where Rayleigh wave FM excitation is low and therefore interference is unusually strong. Our analysis also reinforces the dependence of the interference on the FM and overtone group velocities. For Love waves, this results in weak minor-arc overtone interference at long periods and, for continental paths, short periods. For Rayleigh waves, the differing overtone and FM group velocities and the relative excitation of the overtones and FM explain rapid variations in the strength of Rayleigh wave major-arc overtone interference as a function of epicentral distance. We then show that real data are affected by the relative excitation of the FM and overtones. We find that errors in Rayleigh wave phase velocities determined at the EarthScope USArray stations are larger when the ratios of overtone to FM excitation are larger. We also find a dependence of phase velocity error on excitation ratio for Love waves, and we identify the presence of major-arc overtone interference in Love wave measurements. Our results highlight opportunities for more nuanced quality control of surface wave measurements. The relative excitation ratio of the overtones and FM may be a better criterion for event selection than source depth, allowing deeper events that well excite FMs to be included and shallower events with large overtone excitation to be excluded. This would allow the collection of more accurate measurements that will increase the precision of seismic images.

Line parameters of the 4-0 band of carbon monoxide by high sensitivity cavity ring down spectroscopy near 1.2 µm

The room temperature spectrum of the very weak third overtone band of carbon monoxide in natural isotopic abundance is recorded by cavity ring down spectroscopy (CRDS) referenced to a frequency comb, between 8206 and 8465 cm−1. The sensitivity of the recordings (noise equivalent absorption on the order of αmin ∼ 5 × 10−12 cm−1) allowed for measuring lines with intensity as weak as 1 × 10−30 cm/molecule at a recording pressure limited to 10.0 Torr. The use of low pressure values (1.0 and 10.0 Torr) helped to minimize the impact of profile effects on the derived line positions and line intensities. The line profile analysis was performed using the speed dependent Nelkin-Ghatak model for the 10 Torr recordings while the Voigt profile was found sufficient to account for the line shapes recorded at 1.0 Torr.Overall, line parameters of 227 transitions are derived. The observed transitions belong to the 4-0 band of the 12C16O, 13C16O, 12C18O and 12C17O isotopologues present in natural abundance in the sample and to the 5-1 hot band of 12C16O. For a large part of the observations, line positions are reported with accuracy as good as 4 × 10−6 cm−1 (∼120 kHz). The self-induced line shift of the 4-0 band is reported for the first time from the position values at 1 and 10 Torr. Using literature values of the 1-0, 2-0 and 3-0 bands, the vibrational dependence of the self-induced pressure shift in CO is discussed. The experimental values of the 12C16O v = 4 energy levels J < 26 are reproduced with a standard deviation of 2.5 × 10−6 cm−1 (75 kHz). The intensities of the 12C16O lines reported with an accuracy better than 1% show an overall good agreement with literature values in particular with those included in the HITRAN database.

УЛЬТРАДЫБЫС ЖАҒДАЙЫНДА 4-АМИНОБЕНЗОЙ ҚЫШҚЫЛЫНЫҢ МОДИФИКАЦИЯЛАНҒАН ТУЫНДЫСЫН СИНТЕЗДЕУ

The search for new effective drugs with biologically active properties is one of the urgent problems. Recently, to intensify the process of their synthesis and increase the efficiency of chemical reactions, wave chemistry has been used. Increased interest of researchers is caused by the synthesis of compounds with biologically active properties using the method of ultrasonic treatment (US). It is known that derivatives of p-aminobenzoic acid and their esters are synthetic analogues of natural compounds, and pyrrolidone derivatives have high hypnotic, anticonvulsant, antiarrhythmic activity, which stimulates the synthesis of new biologically active compounds. In a brief report, the possibility of synthesizing ethyl-4-(2,5-dioxo-2,5-dihydro-1H-pyrrolyl) benzoate from 3-[(4-ethoxycarbonyl) phenylcarbamoyl]-2-propenoic acid using ultrasonic activation through a step is considered disclosure of the furan cycle with further cyclization. Ethyl ester p-aminobenzoic acid and maleic anhydride were used as starting reagents. An ultrasound device IL-100-6/2, equipped with a magnetostrictive transducer, with an operating frequency of 22 kHz, with a maximum power of 1200 W and a cylindrical waveguide, was used as a source of ultrasound. The synthesis of 3-[(4-ethoxycarbonyl) phenylcarbamoyl]-2-propenoic acid was carried out by reacting the starting reagents at equimolar ratios and room temperature. The US time was 10 minutes. The reaction proceeds smoothly. Ultrasound has a significant effect on the rate of chemical reactions and can increase the yield of the final product. Under classical conditions, the synthesis time was 180 minutes; using ultrasound, the synthesis time was reduced by 3 times. The product yield was 92%. The structure and composition of the obtained compound was confirmed by IR- and H1 NMR-spectroscopy. In the IR-spectra of the obtained compound, there are absorption bands of the amide group (NHCO) in the region of 3280, 3190 cm-1, absorption bands of the carbonyl group (C=O), characteristic in the region of 1670 cm-1, absorption band (COC) in the region of 1230 cm-1. The resulting compound, 3-[(4-Ethoxycarbonyl) phenylcarbamoyl]-2-propenoic acid, made it possible to study the step of opening the furan ring, with further cyclization. Ethyl 4-(2,5-dioxo-2,5-dihydro-1H-pyrrolyl) benzoate was obtained in 89% yield by azeotropic distillation of water in the presence of toluenesulfonic acid in a DMFA-toluene mixture. The resulting product is a light yellow powder with melting point 114-115°C. The structure and composition of the obtained compound was confirmed by IR-and H1 NMR-spectroscopy. In the IR-spectra of the obtained compound, the stretching vibrations of the НС=СН group manifest themselves in the form of a low-intensity but characteristic signal at 3100-3090 cm-1, stretching vibrations of the С=О group as intense bands in the region of 1700-1680 cm-1 and a weak overtone at 3465-3450 cm-1, stretching vibrations of the COC group in the region of 1245 cm-1. When analyzing the Н1 NMR-spectrum of a compound, ethyl 4-(2,5-dioxo-2,5-dihydro-1Н-pyrrolyl) benzoate, the signals of aromatic four protons Н1- Н2 (4Нaryl, 3JНН 8 Hz) are recorded in the field of weak fields: H1 doublet at 7.51 ppm. and a doublet at 8.05 ppm. Signals of the ethyl fragment: (3H, CH3, 3JHH 8 Hz), appear as a singlet at 1.43 ppm. and (2H, CH2, 3JHH 8 Hz) quadruplet at 4.34 ppm. The protons of the CH group of the imide cycle (2H, CH=CH) appear as a singlet at 7.11 ppm. Keywords: ultrasound, ethyl ether p-aminobenzoic acid, maleic anhydride, cyclization.

High-Q surface electromagnetic wave resonance excitation in magnetophotonic crystals for supersensitive detection of weak light absorption in the near-infrared

The mid-infrared spectrum can be recorded from almost any material, making mid-infrared spectroscopy an extremely important and widely used sample characterization and analysis technique. However, sensitive photoconductive detectors operate primarily in the near-infrared (NIR), but not in the mid-infrared, making the NIR more favorable for accurate spectral analysis. Although the absorption cross section of vibrational modes in the NIR is orders of magnitude smaller compared to the fundamental vibrations in the mid-infrared, different concepts have been proposed to increase the detectability of weak molecular transitions overtones. Yet, the contribution of magnetophotonic structures in the NIR absorption effect has never been explored so far. Here we propose high-Q magnetophotonic structures for a supersensitive detection of weak absorption resonances in the NIR. We analyze the contributions of both magnetic and nonmagnetic photonic crystal configurations to the detection of weak molecular transitions overtones. Our results constitute an important step towards the development of highly sensitive spectroscopic tools based on high-Q magnetophotonic sensors.

Differential extinction of vibrational molecular overtone transitions with gold nanorods and its role in surface enhanced near-IR absorption (SENIRA).

Resonant coupling between plasmonic nanoantennas and molecular vibrational excitations is employed to amplify the weak overtone transitions that reside in the near-infrared. We explore for the first time the differential extinction of forbidden molecular overtone transitions coupled to the localized surface plasmons. We show a non-trivial interplay between the molecular absorption enhancement and suppression of plasmonic absorption in a coupled system. When the resonance conditions are met at 1.5 μm, two orders of magnitude enhancement of differential extinction as compared to the extinction of the same amount of free probe molecules is achieved. Our results pave a road toward a new class of surface enhanced near-infrared absorption-based sensors.

Tuning the Near-Infrared Absorption of Aromatic Amines on Tapered Fibers Sculptured with Gold Nanoparticles

We discover an unexpected enhancement of the absorption of near-infrared light by aromatic amine overtones on photonic microfibers sculptured with gold nanoparticles. The adsorbed nanoparticles make the near-infrared spectroscopy of aromatic amines on microfibers feasible despite the small absorption cross-section of the molecular vibration overtones. We demonstrate that in the presence of gold nanomediators, the absorption of light by weak overtone transitions in N-methylaniline as a model analyte is dramatically enhanced. We attribute this effect to the increase of the mean trajectory of light in a microfiber due to its resonant scattering on metallic nanoparticles. The spectrally integrated transmittance scales with the concentration of nanoparticles to the power 1/6—the phenomenon of diffusive propagation of light. Practical applications of the discovered effect will include the detection of aromatic amines for efficient treatment of metabolic disorders resulting from the amino acids deficiency, resea...

Quantum cascade laser spectroscopy of OCS isotopologues in 4He nanodroplets: A test of adiabatic following for a heavy rotor.

We report high-resolution infrared spectra of OCS isotopologues embedded in helium nanodroplets that were recorded with a newly built spectrometer. For the normal isotopologue, we observed the relatively weak third bending overtone band, in addition to new high J transitions in the C-O stretching fundamental, which has previously been investigated by diode laser spectroscopy [S. Grebenev et al., J. Chem. Phys. 112, 4485 (2000)]. Similar to the gas phase, the overtone band is (only) 45 cm-1 higher in energy than the fundamental, and this leads to additional broadening due to rapid vibrational relaxation that is accompanied by the creation of real/virtual phonon excitations. We also observed spectra in the C-O stretching fundamental for several minor isotopologues of OCS, including 18OCS, O13CS, and OC33S, in addition to some new peaks for OC34S. A rovibrational analysis allowed for determination of the moment of inertia of helium (ΔIHe) that couples to the rotation of OCS for each isotopologue. In the context of the adiabatic following approximation, the helium density structure that follows the rotation of OCS should essentially remain unchanged between the isotopologues, i.e., there should be no dependence of ΔIHe on the gas phase moment of inertia of OCS (IG). While this behavior was expected for the "heavy" OCS rotor investigated here, we instead found an approximately linear 1:1 relation between ΔIHe and IG, which suggests partial breakdown of the adiabatic following approximation, making OCS the heaviest molecule for which evidence for this effect has been obtained.

Near-infrared absorption gas sensing with metal-organic framework on optical fibers

Despite significant advantages in terms of portability and cost, near-infrared (NIR) gas sensing still remains a great challenge due to its relatively weak overtone absorption from the fundamental vibrational bond absorption at the mid-IR frequency. In this paper, we demonstrated ultra-sensitive NIR gas sensing for carbon dioxide (CO2) at 1.57μm wavelength through nanoporous Cu-BTC (BTC=benzene-1,3,5-tricarboxylate) metal-organic framework (MOF) coated single-mode optical fiber. For the first time, we obtained high-resolution NIR spectroscopy of CO2 sorbed in MOF without seeing any rotational side band, indicating that the tightly confined gas molecules in the MOF pores do not have any freedom of rotation. Real-time measurement of the mixed gas flow of CO2 and Ar showed different response time depending on the concentration of CO2, which is attributed to the complex sorption mechanism of CO2 in Cu-BTC MOF. Most importantly, we realized ultra-low detection limit of CO2 (<20ppm) with only 5cm long Cu-BTC MOF thin film coated on single-mode optical fibers.

Sound spectrum of a pulsating optical discharge

A spectrum of sound of an optical discharge generated by a repetitively pulsed (RP) laser radiation has been investigated. The parameters of laser radiation are determined at which the spectrum of sound may contains either many lines, or the main line at the pulse repetition rate and several weaker overtones, or a single line. The spectrum of sound produced by trains of RP radiation comprises the line (and overtones) at the repetition rate of train sequences and the line at the repetition rate of pulses in trains. A laser with the pulse repetition rate of and the average power of up to was used in the experiments.

Incoherent broadband cavity enhanced absorption spectroscopy using supercontinuum and superluminescent diode sources.

We investigate incoherent broadband cavity enhanced absorption spectroscopy using a tailored supercontinuum source. By tailoring the supercontinuum spectrum to match the high reflectivity bandwidth of the mirrors, we achieve an unprecedented spectral brightness of more than 7 dBm/nm at wavelengths where the effective absorption path length in the cavity exceeds 40 km. We demonstrate the potential of the source in spectrally broadband measurement of weak overtone transitions of carbon dioxide and methane in the near-infrared 1590 nm - 1700 nm range and evaluate its performance against that of a typical superluminescent diode source. Minimum detectable absorption coefficients (3σ) of 2.2 × 10(-9) cm(-1) and 6.2 × 10(-9) cm(-1) are obtained with the supercontinuum and the superluminescent diode sources, respectively. We further develop a spectral fitting method based on differential optical absorption spectroscopy to fully and properly account for the combined effect of absorption line saturation and limited spectral resolution of the detection. The method allows to cope with high dynamic range of absorption features typical of real-world multi-component measurements.

Picosecond dynamics of photoexcited DNO-bound myoglobin probed by femtosecond vibrational spectroscopy.

Like nitric oxide (NO), nitroxyl (HNO), a reduced form of NO, plays many biologically important roles including neurological function and vascular regulation. Although HNO is unstable in aqueous solution, it is exceptionally stable on binding to ferrous myoglobin (Mb) to form MbHNO. Various experimental and theoretical investigations has been carried out to unveil the structure of the active site and binding characteristics of MbHNO that can explain its functioning mechanism and the origin of its unusual stability. However, the binding dynamics of HNO to Mb, as well as the photochemical and photophysical processes associated with binding, have not been fully established. Herein, femtosecond vibrational spectroscopy was used to probe the photoexcitation dynamics of excited MbDNO in D2O solution at 294 K with a 575 nm pulse. Time-resolved spectra were described by three vibrational bands near 1380 cm(-1), in the expected N-O stretching (νN-O) mode of MbDNO, and all three bands showed instantaneous bleach that decays on a picosecond time scale. The three bands were assigned based on isotope shifts upon (15)N substitution and ab initio calculation of the vibrational frequency on a DNO-bound model heme. These three bands likely arise from Fermi interactions between the strong νN-O mode and the weak overtone and combination modes of the N atom-related modes. The immediate appearance of the bleach in these bands and the picosecond decay of the bleach indicate that most of the photoexcited MbDNO undergoes picosecond geminate rebinding (GR) of DNO to Mb subsequent to its immediate deligation. Ultrafast and efficient GR of DNO likely arises from the bonding structure of the ligand and high reactivity between DNO and Mb.

Fundamental and overtone vibrational spectroscopy, enthalpy of hydrogen bond formation and equilibrium constant determination of the methanol–dimethylamine complex

We have measured gas phase vibrational spectra of the bimolecular complex formed between methanol (MeOH) and dimethylamine (DMA) up to about 9800 cm(-1). In addition to the strong fundamental OH-stretching transition we have also detected the weak second overtone NH-stretching transition. The spectra of the complex are obtained by spectral subtraction of the monomer spectra from spectra recorded for the mixture. For comparison, we also measured the fundamental OH-stretching transition in the bimolecular complex between MeOH and trimethylamine (TMA). The enthalpies of hydrogen bond formation (ΔH) for the MeOH-DMA and MeOH-TMA complexes have been determined by measurements of the fundamental OH-stretching transition in the temperature range from 298 to 358 K. The enthalpy of formation is found to be -35.8 ± 3.9 and -38.2 ± 3.3 kJ mol(-1) for MeOH-DMA and MeOH-TMA, respectively, in the 298 to 358 K region. The equilibrium constant (Kp) for the formation of the MeOH-DMA complex has been determined from the measured and calculated transition intensities of the OH-stretching fundamental transition and the NH-stretching second overtone transition. The transition intensities were calculated using an anharmonic oscillator local mode model with dipole moment and potential energy curves calculated using explicitly correlated coupled cluster methods. The equilibrium constant for formation of the MeOH-DMA complex was determined to be 0.2 ± 0.1 atm(-1), corresponding to a ΔG value of about 4.0 kJ mol(-1).

Laser-induced grating spectroscopy of highly excited overtone and combination vibrational states of methane

Laser-induced grating spectroscopy is applied to investigate weak overtone and combination absorption bands of methane. The rotationally-resolved spectra of transitions to the polyads Pn, n=8–10, 12 recorded at pressures ranging from 0.2 to 4bar and temperatures 298K and 124–130K cover a broad interval between 891 and 618nm (11220–16180cm−1) and contain a significant amount of prominent narrow lines which correspond to stationary rovibrational states. The absorption cross sections of the weakest detected methane transitions are estimated to be as small as ≈10−26cm2molecule−1. The technique is suitable to provide data for the development and verification of new models describing the complex energy structure of highly vibrationally excited molecules.

Spectroscopic study of self and buffer gas broadened CO2 overtone transitions at 780 nm by NIR diode laser spectrometer

A high resolution near infrared (NIR) diode laser spectrometer along with a multipass cell is used to detect weak rovibronic transitions of carbon dioxide in the NIR region. The self, nitrogen and air broadening line shape parameters of three rovibrational transitions P(44), P(46) and P(48) of 12C16O2 belonging to the (ν1 + 5 ν3) overtone band around 780 nm are studied. Wavelength modulation spectroscopy with phase sensitive detection technique at the first harmonic is used to detect the weak overtone transitions of CO2. The observed line shapes are fitted with the standard Voigt profile by a non-linear least squares fitting program in order to determine the self and buffer gas (air and N2) broadening coefficients and line strength parameters of the CO2 transitions. The O2 broadening coefficients are calculated from the experimentally measured N2 and air broadening coefficient values. The measured parameters are compared with the available experimental data and a reasonable agreement has been found.