Single photon infrared emission spectroscopy of the gas phase pyrene cation: support for a polycyclic aromatic hydrocarbon origin of the unidentified infrared emission bands.

We report the first observation of infrared emission from a gaseous ionic polycyclic aromatic hydrocarbon (PAH), the pyrene cation, over the range of wavelengths spanned by the ubiquitous interstellar unidentified infrared emission bands (UIRs). The complete set of pyrene cation IR emissions is observed, with relative intensities consistent with astrophysical observations, supporting the proposal that ionized PAHs are major contributors to the UIR bands. Additionally, unidentified features possibly arising from dehydrogenated PAH species are noted in the spectrum.     

The Vibrational Spectra of 9-Fluorenone and Some of Its Isotopic Isomers

Abstract

Vibrational spectra of 9-Fluorenone, 9-Fluorenone-¹⁸O and 9-Fluorenone-d₈ have been recorded in the solid state and solutions in the infrared and (4000–100 cm^?1) and in the Raman (4000–50 cm^?1). Differential infrared linear dichroic spectra have also been measured. The assignment of the vibrational bands is performed using the group vibrational concept, isotopic shifts and polarization features of the normal modes.     

Raman spectra of submicron amorphous carbon grains and mixtures of polycyclic aromatic hydrocarbons

We present here Raman spectra of different samples of materials, potentially candidates of interstellar dust, namely amorphous carbon submicron particles and polycyclic aromatic hydrocarbon collections (PAH). The carbon particles show spectra characterized by two peaks, falling respectively at 1365 cm⁻¹ and 1590 cm⁻¹, while PAH spectra seem to be characterized by a single line at 1590 cm⁻¹.These preliminary results confirm that PAH collections alone cannot account for the astronomical unidentified infrared bands (UIR), while mixtures containing also hydrogenated amorphous carbon (HAC) produce a better match.     

The stretching–bending bands of 13C2HD

The infrared spectrum of ¹³C₂HD has been investigated using high-resolution Fourier transform infrared spectroscopy. A large number of ro-vibrational transitions in the spectral region 1000–6600?cm^?1 have been recorded and assigned. This paper is focused only on the vibrational bands involving pure stretching, stretching–bending or stretching–stretching modes. In total, 78 bands have been identified and assigned, 29 related to υ₁(CH stretch), 27 to υ₂(CC stretch), and 22 to υ₃(CD stretch). The data pertaining to each stretching mode have been fitted simultaneously in order to obtain accurate sets of rotational and vibrational parameters for the excited states.     

The infrared spectrum of 12C2HD: the stretching–bending combination bands in the 1800–4700 cm−1 region

The infrared spectrum of ¹²C₂HD has been observed between 1800 and 4700?cm^?1 by Fourier transform spectroscopy. The ν₁, ν₂ and ν₃ absorption bands and the associated hot and combination bands involving the bending modes up to υ_t?=?υ₄?+?υ₅?=?2 have been investigated. Altogether, 60 vibrational bands were analysed, leading to the spectroscopic characterization of 31 vibrationally excited states. Several perturbations have been observed, but the transitions involving the perturbing states have not been detected. As a consequence, an appropriate treatment of the vibrational or ro-vibrational interactions has not been possible. A tentative assignment of the perturbing states has been proposed. Eventually, global fits for each fundamental vibration and its associated cold and hot bands have been performed.     

High temperature arc studies of infrared radiation from boron and tungsten oxides

Long wavelength infrared emission spectra from boron and tungsten compounds in air were obtained in a d.c. arc jet at 3000–6000°K for the wavelength range 1·2–24 μm. Absolute vibrational band intensities were measured for WO, WO₂, WO₃, BO, BOF and BF₃ molecules. Several unidentified bands were observed and are discussed.     

Band analysis of the Swan system (d3Πg-a3Πu) of 13C2 and 12C13C molecules

The emission spectrum of the d³Π_g-a³Π_u system (Swan bands) due to ¹³C₂ and ¹²C¹³C molecules has been obtained in a low pressure hollow cathode discharge through a mixture of argon and benzene containing enriched ¹³C (90%). The spectrum was photographed on a 3.4-m Ebert spectrograph (reciprocal dispersion 0.54 Å mm^?1 in the first order). Isotope effect measurements have been carried out to determine the shift between isotopic bands and those emitted by ordinary molecules. The rotational analysis of six ¹³C₂ bands and three bands of ¹²C¹³C has been performed and molecular constants were derived.     

The infrared spectrum of 13C2HD between 100 and 2100 cm−1: a global fit for the bending states up to υ 4 + υ 5 = 3

The fundamental bending ro-vibrational bands and a number of overtone, combination and hot bands of ¹³C₂HD have been recorded by Fourier transform infrared spectroscopy in the range 450–2100 cm^?1. In addition, the ν ₅ ← ν ₄ band, centred at 164.65 cm^?1, has been identified in the spectrum of ¹³C₂H₂. The data were analysed simultaneously in a global fit that has provided very accurate rotational and vibrational parameters for the ground and vibrationally excited states.     

High-Resolution Fourier Transform Infrared Spectrum of the ν1+ν3 Band System of HCCH

A high-resolution vibration-rotation overtone spectrum of H¹³C¹²CH has been recorded with a Fourier transform infrared spectrometer in the wavenumber region 6400 to 6700 cm⁻¹. The main band, assigned as the C-H stretching combination band ν₁+ν₃, and some overtone and hot bands have been rotationally analyzed. Altogether eight parallel bands have been observed. The vibrational labels have been deduced on the basis of the assignments of the fundamental ν₃ antisymmetric C-H stretching band system.     

Band analysis of the Swan system (dΠg-aΠu) of C2 and CC molecules

The emission spectrum of the d³Π_g-a³Π_u system (Swan bands) due to ¹³C₂ and ¹²C¹³C molecules has been obtained in a low pressure hollow cathode discharge through a mixture of argon and benzene containing enriched ¹³C (90%). The spectrum was photographed on a 3.4-m Ebert spectrograph (reciprocal dispersion 0.54 Å mm⁻¹ in the first order). Isotope effect measurements have been carried out to determine the shift between isotopic bands and those emitted by ordinary molecules. The rotational analysis of six ¹³C₂ bands and three bands of ¹²C¹³C has been performed and molecular constants were derived.     

Isotopic fractionation between gaseous and condensed carbon dioxide

The isotopic fractionation in the equilibrium liquid-vapour system of carbon dioxide has been measured for both the carbon and oxygen isotopic species in the temperature range 220–303 °K (Fig. 1). The¹²C¹⁶O¹⁸O isotopic species is somewhat less, and¹³C¹⁶O₂ slightly more volatile than¹²C¹⁶O₂, while the fractionation in both cases approaches zero at the critical temperature. The theoretical expression derived for isotopic fractionation in two phase equilibria qualitatively accounts for the observed direction of the enrichment but fails to explain its disappearance at the critical point. A temperature dependence of the binding energy and intermolecular vibration frequency is proposed to bring the theory into accordance with observation. The magnitude of the unknown term in the fractionation caused by internal effects (including hindered rotation) is obtained by subtraction. It is of the same order of magnitude as the other terms.     

Interferometric determination of the dispersion of the vibrational polarizability and the integral intensities of fundamental bands of trifluorochloromethane molecules CF<Subscript>3</Subscript>Cl

Using two-color interferometry, the dispersion of the refraction and the vibrational polarizability of freon molecules CF₃Cl of natural isotopic composition was studied in the lasing range of an IR laser on the basis of the main isotopomer of carbon dioxide (¹²C¹⁶O₂). Simultaneous processing of the data of the absolute refractometric and relative absorption measurements using the Kramers-Kronig formalism made it possible to refine the integral intensities of the fundamental vibrational bands ν₁ and ν₄ and to determine the dispersion of the vibrational polarizability in the range from 1050 to 1250 cm^?1.     

The infrared spectrum of 12C2HD: the bending states up to υ4 +υ5 =3

The infrared spectrum of ¹²C₂HD has been recorded at high resolution between 450 and 2100?cm^?1 by Fourier transform spectroscopy. The ν₄ and ν₅ bending fundamental bands together with overtones, combination bands and associated hot bands involving modes up to υ_tot?=?υ₄?+?υ₅?=?3 have been identified. Altogether, 43 vibrational bands have been analysed, leading to the spectroscopic characterization of the ground state and of 18 vibrationally excited states. They include all the components of the vibrational manifolds up to υ_tot?=?3, with the exception of the υ₄?=?3, ??=?±3 state. A simultaneous fit of all the assigned transitions has been performed. The adopted model includes vibration and rotation ?-type interaction resonances. The determined spectroscopic parameters reproduce the assigned wavenumber transitions with RMS values close to the estimated experimental uncertainties.     

Analysis of the high-resolution infrared spectrum of cyclopropane

The high-resolution infrared spectrum of cyclopropane (C₃H₆) has been measured from 100 cm⁻¹ to 2200 cm⁻¹. In that region we have identified 24 absorption bands attributed to six fundamental bands, five combination bands, three hot bands and 10 difference bands. Long pathlength spectra, up to 32 m, facilitated the identification and analysis of many previously unstudied infrared inactive, and Raman and infrared inactive vibrational states, including direct access to two forbidden fundamental states, ν₄ and ν₁₄. An improved set of constants for the ground vibrational state as well as for the fundamental vibrations ν₇, ν₉, ν₁₀, ν₁₁ are also reported. The spectral resolution of the measurements varied from 0.002 cm⁻¹ to 0.004 cm⁻¹.     

IR Spectrum of C8H2: Integrated Band Intensities and Some Observational Implications

Polyynes are of astrophysical interest since they appear to be involved in organic chemistry in very different mediums. In Titan's atmosphere, the lightest polyyne, C₄H₂, was detected by Voyager. Recently C₄H₂ and C₆H₂ have been discovered in a protoplanetary nebula, suggesting polyynes as a possible chemical pathway to PAH (polycyclic aromatic hydrocarbons). Moreover, several experimental simulations and modeling imply their production from the photochemistry of methane and their involvement in the formation of organic aerosols. After the study of C₄H₂ and C₆H₂ spectra in the UV and IR wavelength range, we report here the first spectrum of gaseous C₈H₂ in the range 400–4000 cm⁻¹ at room temperature and low resolution. The task was hardly achieved because of the high instability of this molecule with temperature and pressure. To avoid exothermic polymerization, the compound as mixed with a solvent. We have performed a separate spectroscopic study of the solvent to determine C₈H₂ partial pressure within the mixture. This allowed us to calculate C₈H₂ integrated band intensities. In the studied wavelength range, C₈H₂ presents three main bands similar to those of C₆H₂ in terms of vibrational type, position, and relative intensity. To study the possible identification of these polyynes by spatial observatories (Cassini–Huygens, ISO), we have also measured the C₆H₂ and C₈H₂ infrared spectra in the range 400–1500 cm⁻¹ at 0.35 cm⁻¹ resolution.     

The infrared spectra of 12C32S, 12C34S, 13C32S,and 12C33S

Using a tunable diode laser spectrometer, the infrared absorption spectra of four isotopic species of carbon monosulfide have been observed in the positive column of a dc discharge of CS₂ and Ar. The wavenumbers of 115 vibration-rotation transitions between 1180.5 and 1266.1 cm^?1 have been measured. These lines were assigned to the 1-0, 2-1, 3-2, and 4-3 bands of ¹²C³²S, the 1-0 and 2-1 bands of ¹²C³⁴S and ¹³C³²S, and the 1-0 band of ¹²C³³S. These new data have been combined with the previous infrared and microwave results to determine Dunham coefficients (Y_ij), the Dunham potential expansion constants (a₀,a₁,a₂,a₃, and a₄), and the classical turning points by the RKR method.     

Vibrational Assignment of 2-Benzoyl Pyridine and its 18O Labelled Isomer

Abstract

Vibrational spectra of 2-benzoyl pyridine and 2-benzoyl pyridine-¹⁸O have been recorded in the solid and molten state in the infrared (4000–100 cm^?1) and in the Raman (4000–50 cm^?1). Polarized Raman spectra in the molten state have also been measured. The assignment of the vibrational bands is performed using the group vibrational concept, isotopic shifts and polarization features of the normal modes.     

Millimetre-wave and Fourier transform infrared spectra between 325 cm−1 and 4720 cm−1 of BrCN and global rovibrational analysis of the main isotopomers

The infrared absorption spectrum of BrCN has been recorded in the re?ion 325–4720 cm^?1 with a Bruker 120 HR interferometer. More than 30 000 lines have been measured and most of them have been assigned: 10734 lines for 151 bands and 10993 lines for 150 bands of ⁷⁹Br¹²C¹⁴N and ⁸¹Br¹²C¹⁴N, respectively. Also new millimetre-wave spectra were measured for the vibrational excited states lying between 1000 cm^?1 and 1400 cm-′. After a band by band analysis of these transitions, rovibrational global analyses have been performed for both isotopomers using all available experimental data. The rotational I-type resonance and the anharmonic resonance associated with k_l22 are taken into account in one-step diagonalization procedures. Sets of 73 molecular parameters are obtained for both isotopomers. It is shown that the existing equilibrium structure is likely to be reliable. The vibrational dependence of the quartic centrifugal distortion constant is analysed for the linear triatomic molecules studied so far.     

Study of isotopic 13C2 bands of the Deslandres-D'Azambuja system

The emission bands of the Deslandres-D'Azambuja system of ¹³C₂ have been obtained in the region 320–450 nm using a source containing enriched ¹³C. Measured line positions of the 2-0, 2-1, 1-0, 0-0, 1-1, 1-0, 2-1, and 3-2 bands were fitted by a least-squares procedure to determine the rotational constants and the origin for each band. The fitted origins were used as input in calculation of the vibrational constants for both C¹Π_u electronic states involved in the transition.