High-resolution FTIR spectroscopy of the ν8 and Coriolis perturbation allowed ν12 bands of ketenimine

High resolution FTIR spectra have been recorded in the region 250-770 cm(-1) using synchrotron radiation and over 2000 transitions to the ν(8) and ν(12) states of the short lived species ketenimine have been assigned. Ground state combination differences combined with published microwave transitions were used to refine the constants for the ground vibrational state. Rotational and centrifugal distortion parameters for the v(8) = 1 and v(12) = 1 levels were determined by co-fitting transitions, and treating a strong a-axis Coriolis interaction. Selection rules for the observed ν(12) transitions indicate that they arise solely from "perturbation allowed" intensity resulting from this Coriolis interaction.     

High-resolution Fourier-transform infrared spectroscopy of the Coriolis coupled ground state and ν7 mode of ketenimine

High resolution FTIR spectra of the short lived species ketenimine have been recorded in the regions 390-1300 cm(-1) and 20-110 cm(-1) using synchrotron radiation. Two thousand six hundred sixty transitions of the ν(7) band centered at 693 cm(-1) and 126 far-IR rotational transitions have been assigned. Rotational and centrifugal distortion parameters for the ν(7) mode were determined and local Fermi and b-axis Coriolis interactions with 2ν(12) are treated. A further refinement of the ground state, ν(12) and ν(8) parameters was also achieved, including the treatment of previously unrecognized ac-axis and ab-axis second order perturbations to the ground state.     

High-resolution Fourier transform infrared absorption spectroscopy of the ν6 band of c-C3H2

The gas-phase high-resolution absorption spectrum of the ν(6) band of cyclopropenylidene (c-C(3)H(2)) has been observed using a Fourier transform infrared spectrometer for the first time. The molecule has been produced by microwave discharge in an allene (3.3 Pa) and Ar (4.0 Pa) mixture inside a side arm glass tube. The observed spectrum shows a pattern of c-type ro-vibrational transitions in which the Q-branch lines strongly and distinctly stand out in the spectrum. A combined least-squares analysis of the observed 216 ro-vibrational transitions together with 28 millimeter-wave rotational transitions from the previous study has resulted in an accurate determination of the molecular constants in the ν(6) state. The band center is found to be at 776.11622(13) cm(-1) with one standard deviation in parentheses, which is 2.3% lower than the matrix isolation value. The intensity ratio I(3)(ν(3))/I(6)(ν(6)) obtained from the observed ν(3) and ν(6) bands, 1.90(9), is somewhat lower than the ratio estimated from ab initio (2.4-2.6) and DFT (2.8) calculations.     

High-resolution Fourier transform infrared spectroscopy and analysis of the ν12 fundamental band of ethylene-d4

The Fourier transform infrared (IR) spectrum of the ν₁₂ fundamental band of ethylene-d₄ (C₂D₄) has been measured with an unapodized resolution of 0.004 cm⁻¹ in the frequency range of 1030–1130 cm⁻¹. A total of 1340 assigned transitions have been analyzed and fitted using a Watson's A-reduced Hamiltonian in the I^r representation to derive rovibrational constants for the upper state (v₁₂=1) up to five quartic terms with a standard deviation of 0.00042 cm⁻¹. They represent the most accurate constants for the band thus far. The ground state rovibrational constants were also further improved by a fit of combination–differences from the IR measurements. The relatively unperturbed band was found to be basically A-type with a band centre at 1076.98492±0.00003 cm⁻¹.     

Vibration-rotation infrared spectrum of ν2 of methyl iodide—Coriolis interaction with ν5

Vibration-rotation i.r. spectrum of ν₂ of methyl iodide was measured with a resolution of 0.08 cm⁻¹. The spectrum was analyzed by taking account of an xy-type Coriolis interaction between ν₂ and ν₅ and a Fermi resonance between ν₅ and ν₃ + ν₆. The analysis gave values of spectroscopic parameters which include (ν₀)₂ 1251.193 cm⁻¹, A₂-A₀ 0.02030 cm⁻¹, (D_J)₂ 2.08 × 10⁻⁷ cm⁻¹, (D_JK)₂ 3.2 × 10⁻⁶ cm⁻¹ and ζ_2,5a^y −0.630₅.     

Synchrotron far infrared spectroscopy of the ground, ν(5), and ν(15) states of thiirane

The high-resolution (0.001 cm(-1)) spectrum of thiirane has been recorded at the far-infrared beamline at the Australian synchrotron between 760-400 cm(-1) and 170-10 cm(-1). Ro-vibrational transitions of the highly Coriolis coupled ν(5) (628.1 cm(-1)) and ν(15) (669.7 cm(-1)) fundamentals, as well as pure rotational far-IR transitions have been assigned, and rotational, centrifugal distortion, and Coriolis interaction parameters determined. ν(15) gains the vast majority of its intensity from an interesting Coriolis intensity stealing mechanism, which is also outlined.     

Study of the ν1, ν1 + ν3 and ν2 + ν3 infrared bands of ONCl

A type (ΔK_a = 0) rovibrational lines of the near-prolate asymmetric top ¹⁶O¹⁴N³⁵Cl have been assigned on high resolution Fourier transform spectra: 820 lines of the ν₁ band, centered around 1800 cm⁻¹, 435 lines of the ν₁ + ν₃ band, centered around 2131 cm⁻¹, and 257 lines of the ν₂ + ν₃ band, centered around 925 cm⁻¹. Least-squares calculations have been carried out over these lines, using the A reduced Watson's hamiltonian in I^r representation; r.m.s. standard deviations of 0.0016 cm⁻¹, 0.0016 cm⁻¹ and 0.006 cm⁻¹ have been respectively obtained, making it possible to measure molecular constants of the (001), (101) and (011) vibrational levels of ¹⁶O¹⁴N³⁵Cl.     

Study of the ν2 + ν3 infrared band of ONCl

Two hundred and sixty A type rovibrational lines of the ν₂ + ν₃ vibrational band of ¹⁶O¹⁴N³⁵Cl, around 925 cm⁻¹, have been assigned; a least-squares calculation with a r.m.s. deviation of 0.0006 cm⁻¹ has made it possible to measure several constants of the (011) vibrational level.     

Characterization of macromolecular orientation in κ-carrageenan fibers using polarized Fourier-transform infrared spectroscopy

In the current study, polarized infrared (IR) microspectroscopy was employed to characterize the macromolecular orientation in wet-spun and stretched κ-carrageenan fibers. The fibers were shown to be well oriented by X-ray diffraction, suggesting that the κ-carrageenan molecules were generally aligned along the fiber axis direction. Longitudinal fiber pieces of about 10 μm thick were obtained by focused ion beam (FIB) micromilling. The fiber pieces were examined by polarized IR in transmission mode. Several bands, including those characteristic of κ-carrageenan at 845 and 930 cm⁻¹, were polarization-dependent, demonstrating polarized IR as a useful tool to evaluate macromolecular orientation in carrageenan fibers. Band assignments were discussed by considering the general alignment of molecules and the polarization dependence of vibration modes, and our results agreed well with band assignments from previous reports.     

Submillimeter-wave and far-infrared spectroscopy of high-J transitions of the ground and ν2 = 1 states of ammonia

Complete and reliable knowledge of the ammonia spectrum is needed to enable the analysis and interpretation of astrophysical and planetary observations. Ammonia has been observed in the interstellar medium up to J=18 and more highly excited transitions are expected to appear in hot exoplanets and brown dwarfs. As a result, there is considerable interest in observing and assigning the high J (rovibrational) spectrum. In this work, numerous spectroscopic techniques were employed to study its high J transitions in the ground and ν(2)=1 states. Measurements were carried out using a frequency multiplied submillimeter spectrometer at Jet Propulsion Laboratory (JPL), a tunable far-infrared spectrometer at University of Toyama, and a high-resolution Bruker IFS 125 Fourier transform spectrometer (FTS) at Synchrotron SOLEIL. Highly excited ammonia was created with a radiofrequency discharge and a dc discharge, which allowed assignments of transitions with J up to 35. One hundred and seventy seven ground state and ν(2)=1 inversion transitions were observed with microwave accuracy in the 0.3-4.7 THz region. Of these, 125 were observed for the first time, including 26 ΔK=3 transitions. Over 2000 far-infrared transitions were assigned to the ground state and ν(2)=1 inversion bands as well as the ν(2) fundamental band. Of these, 1912 were assigned using the FTS data for the first time, including 222 ΔK=3 transitions. The accuracy of these measurements has been estimated to be 0.0003-0.0006?cm(-1). A reduced root mean square error of 0.9 was obtained for a global fit of the ground and ν(2)=1 states, which includes the lines assigned in this work and all previously available microwave, terahertz, far-infrared, and mid-infrared data. The new measurements and predictions reported here will support the analyses of astronomical observations by high-resolution spectroscopy telescopes such as Herschel, SOFIA, and ALMA. The comprehensive experimental rovibrational energy levels reported here will permit further refinement of the potential energy surface to improve ammonia ab initio calculations and facilitate assignment of new high-resolution spectra of hot ammonia.     

FTIR spectra of the 2ν4, ν4 + ν6 and 2ν6 bands of formaldehyde

High resolution IR spectra of the overtones and the combination band of the ν₄ and ν₆ modes of formaldehyde (2ν₄, ν₄ + ν₆ and 2ν₆) were measured in the region of 2200–2650 cm⁻¹ using FTIR. The combination band ν₄ + ν₆, whose dipole transition is forbidden from molecular symmetry, was observed due to the intensity borrowed from the other bands. The observed frequencies were analysed by a Hamiltonian in which A-type Coriolis interactions and Darling—Dennison interaction were taken into account. The ratio and the relative signs of the transition dipole moments of the overtone bands, μ_2ν4 and μ_2ν6, have been determined by analysing the intensity distribution of the vibration—rotation lines.     

Rotational and rovibrational spectroscopy of CH3NC of the ground and ν4 = 1 vibrational states

The parallel vibration-rotation band ν(4) of methyl isocyanide (CH(3)NC), with a band center at 944.9 cm(-1), was studied by FTIR spectroscopy between 890 and 980 cm(-1) in order to improve the ground-state rotational constants. Such improvement is essential for the scheduled studies of excited vibrational levels and their mutual anharmonic resonances occurring at higher values of the K rotational number. Ground-state combination differences generated from this band, spanning values of J/K from 0 to 85/13, were combined with rotational data from the literature and newly measured rotational transitions, extending the J/K range from 3/0 up to 31/14, and fitted simultaneously with a fully quantitative reproduction of the data. The infrared data of the ν(4) band were analyzed together with rotational data of the ν(4) = 1 level, spanning values of J/K from 4/0 to 14/12. The fit in the approximation of an isolated vibrational state, with the transitions perturbed by weak local resonances excluded, yields reproduction of the data within experimental uncertainties.     

Raman spectroscopy in the near infrared – a most capable method of vibrational spectroscopy

Raman spectroscopy has enjoyed a dramatic improvement during the last years: The interference by the fluorescence of impurities is virtually eliminated, the sample preparation is considerably easier as for infrared spectroscopy and many applications in routine analytics, quality control and process control in various branches of industry are now possible. It is shown that the up-to-date near-infrared Raman spectrometers now meet most demands for a modern analytical instrument concerning applicability, analytical information and convenience. It can be anticipated that Raman spectroscopy will catch up infrared spectroscopy, the current workhorse of vibrational spectroscopy.     

Study of the spectrum of CH379Br between 1520 and 1700 cm−1: The ν3 + ν6 and the ν5 rovibrational bands

The ν₃ + ν₆ band of CH₃ ⁷⁹Br has been directly analyzed for the first time, and an r.m.s. standard deviation of 0.0035 cm⁻¹ was obtained over 394 lines of K″ΔK = 2 up to 12, through a least-squares calculation using an unperturbed model. Nevertheless discrepancies occur on sub-bands with K″ ⩾ 9, which remain not yet understood. In particular it seems difficult to explain them by a Fermi resonance with the ν₅ band, since it has been possible to fit properly around 580 lines of this band, belonging to sub-bands K″ΔK = 7 up to 16, taking only into account the Coriolis resonance with the ν₂ band and the l(2,2) resonance of ν₅.     

Substituent effects in infrared spectroscopy—XI. Field effects of 4-substituents on the ν(OH) vibrator of isoborneols

The rather low sensitivity to substituent field effects of the free hydroxyl group stretching frequency ν(OH) of a series of 4-X-substituted isoborneols is attributed to the separation of the OH and CX bonds and to the low polarity of the OH bond. The corresponding property of the more polar hydrogen-bonded hydroxyl group is about 40 times more sensitive to substituent variation.     

Raman and infrared study of external and internal vibrational modes of the NO−3 ion isolated in rubidium halides

The vibrational spectra of the NO⁻₃ ion isolated within RbCl, RbBr and RbI has been investigated at various temperatures between 77 and 300 K, by means of i.r. and Raman techniques.At room temperature, the i.r. and Raman activities of the NO⁻₃ internal modes suggest that the NO⁻₃-occupied sites have D₃ symmetry. However at low temperature C_3ν symmetry is suggested.One localized mode has been observed for each system, close to the top of the optic branch of each lattice. They appear at 119, 145 and 166 cm⁻¹ for RbI, RbBr and RbCl respectively. In addition, one gap mode (low density of state mode), centred at 111 cm⁻, has been observed in the uncertain “gap” region between the acoustic and the optic branches of the lattice vibrations of RbCl.     

Illuminating the flesh of bone identification – An application of near infrared spectroscopy

Near infrared (NIR) reflectance spectroscopy coupled with chemometric analysis was evaluated as a non-destructive tool to discriminate skull bone samples from different animal species. In total 70 skull bones from animals of three classes (mammalians, avian and reptiles) were scanned in the wavelength range between 950 to 1650 nm. Principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA) were used to analyse the NIR spectra of the skull samples. Correct classification rates of 96% and 81% were obtained for the classification of skull bone samples according to avian and mammalian classes, respectively. Overall, a 91% correct classification rate was obtained for the classification of skull samples according to the class (mammalian and avian). This study demonstrates the potential of NIR spectroscopy coupled with chemometric as data processing, as a means of a rapid, non-destructive classification technique for skull bone samples.     

Vibrational spectroscopy of lapachol, α- and β-lapachone: Theoretical and experimental elucidation of the Raman and infrared spectra

Raman and infrared spectroscopy were applied for the vibrational characterization of lapachol and its pyran derivatives, α-lapachone and β-lapachone. Experimental spectra of solid state samples were acquired between 4000 and 100 cm⁻¹ in Raman experiments, and between 4000 and 600 cm⁻¹ (mid-infrared) and 600–100 cm⁻¹ (far-infrared) with FTIR spectroscopy, respectively. Full structure optimization and theoretical vibrational wavenumbers were calculated at the B3LYP/6-31 + + G(d,p) level. Detailed assignments of vibrational modes in an experimental and theoretical spectra were based on potential energy distribution analyses, using Veda 4.1 software. Clear differentiation between the three compounds was verified in the region between 1725 and 1525 cm⁻¹, in which the ν(CO) and ν(CC) modes of the quinone moiety were assigned.     

Water adsorption on tin hydrodioxide and its effect on the contour of the infrared absorption band ν(OH)

Tin hydrodioxide SnO₂ · nH₂O (THO, n = 1.5) pellets in potassium bromide were studied by IR absorption spectroscopy. Water adsorption by tin hydrodioxide was shown to give rise to a prominent strong and broad band of stretching vibrations ν(OH) with a peak at 3430 cm^?1. Absorption intensity of this band decreases with distance from the peak rapidly toward higher frequencies and very slowly toward lower frequencies; therefore, the contour is distinguished by very high asymmetry. Analysis of the reasons for this asymmetry taking into account the computer decomposition of the contour into components implies that the unresolved bands from two types of water molecules in THO are superimposed onto the weak bands from two types of hydroxide groups. First type molecules are involved in physisorption to form, with one another, hydrogen bonds that are similar to weak bonds in zeolite and liquid water. Second type molecules are involved in chemisorption and are coordinated to tin ions. Coordination enhances the strengthening of acidic properties and promotes the appearance of strong H-bonds. The peak intensity of the THO ν(OH) band depends primarily on the contribution of vibrational transitions of first type molecules and to a lesser extent on the contribution of vibrational transitions of the first type hydroxide groups. The vibrational transitions in second type molecules and second type groups influence the curvature of the contour on the low-frequency side of the peak.