Infrared Band Intensities Research Articles

Binding Energies and Vibrational Spectral Features of S n Species on Amorphous Water-ice Mantles: A Quantum Mechanical Study

In the denser and colder regions of the interstellar medium (ISM), gas-phase sulfur is depleted by 2 or 3 orders of magnitude with respect to its cosmic abundance. Thus, which species are the main carriers of sulfur is an open question. Recent studies have proposed S n species as potential sulfur reservoirs. Among the various sulfur allotropes, the most stable one is the S8 ring, detected in the asteroid Ryugu and Orgueil meteorite. Shorter species, namely S3 and S4, have been found in the comet 67P/C-G, but their presence in the ISM remains elusive. In this study, we compute the binding energies (BEs) of S n (n = 1–8) species on an amorphous water-ice surface model and analyze their infrared (IR) and Raman spectral features to provide data for their identification in the ISM. Our computations reveal that these species exhibit lower BEs than previously assumed and that their spectral features experience minimal shifts when adsorbed on water ice, because of the weak and nonspecific S n –ice interactions. Furthermore, these species display very low IR band intensities and, therefore, very accurate instruments operating in the mid-IR range are required for detecting the presence of these species in dense interstellar environments.

Vibrational bands of formaldoxime isotopologue 13CD2NOH in the 280–4000 cm−1 region and rovibrational analysis of its [formula omitted] band by Fourier transform infrared (FTIR) spectroscopy

A total of 11 fundamental and 3 overtone bands of the formaldoxime isotopologue 13CD2NOH were identified using its Fourier transform infrared (FTIR) spectra which were recorded with a low resolution (0.50 cm−1) in the 500–4000 cm−1 region, and high resolution (0.00096 cm−1) in the 280–500 cm−1 region. Their relative infrared (IR) band intensities were also measured. Furthermore, a rovibrational analysis of the IR transitions of the ν12 band of 13CD2NOH was carried out using its high-resolution FTIR spectrum which was recorded at the Australian Synchrotron. A total of 1077 IR transitions of the C-type ν12 band were assigned and fitted using the Watson's A-reduced Hamiltonian in the Ir representation to derive its band center and the v12 = 1 state rovibrational constants up to all 5 quartic centrifugal distortion terms for the first time, with a root-mean-square (rms) deviation of 0.00044 cm−1. The band center of the ν12 band of 13CD2NOH were found to be 391.054446(36) cm−1. The ground state rovibrational constants up to all 5 quartic terms were determined for the first time by fitting 407 ground state combination differences (GSCDs) derived from the assigned IR transitions of the ν12 band of 13CD2NOH of this work. The rms deviation of the GSCD fit was 0.00040 cm−1. Additionally, all 3 rotational constants and 5 quartic centrifugal distortion terms of the ground state and 3 rotational constants of the v12 = 1 state of 13CD2NOH were computed from theoretical anharmonic calculations at two different levels of theory, B3LYP and MP2 with the cc-pVTZ basis set, for comparison with the experimental results. Close agreement was found for the calculated and experimental rovibrational constants of 13CD2NOH for both ground and v12 = 1 states. The vibrational anharmonic frequencies of the 12 fundamental bands of 13CD2NOH in the 280–4000 cm−1 region, and their IR band intensities were also calculated using B3LYP and MP2 with the cc-pVTZ basis set, and they were compared with the respective experimental data. Finally, the ground state rotational constants and the band center of the ν12 band of the cis conformer of 13CD2NOH were calculated and compared with those of the trans conformer of this work.

Influence of γ–radiation input dose and post-radiation high temperature shear grinding on polypropylene functional group composition

The effect of γ-irradiation in vacuum and air followed by HTSG of polypropylene (PP) is studied using both infrared (IR) spectroscopy and computational chemistry at the correlated G3(MP2)B3 molecular orbital theory level. γ-irradiation of PP in vacuum was found to primarily induce unsaturation and hydroxyl formation from residual system water whereas γ-irradiation of PP in air oxidizes the polymer and degrades the backbone in a thin layer due to oxygen permeability limitations as supported by the computational thermodynamics results. HTSG of the irradiated PP produced smaller particles than un-irradiated PP. HTSG of the irradiated PP led to a decrease in the IR band intensity from degradation due to a nominal homogenization of the pellet. HTSG of air irradiated PP led to a reduction in IR vibrational band intensity from oxidation due to thermal degradation. High-temperature shear grinding of γ-irradiated PP produces variable chemical and physical composition depending on irradiation input dose and environmental conditions. The combination of γ-irradiation and HTSG may be of benefit in recycling polypropylene.

Fourier transform infrared (FTIR) spectroscopy of formaldoxime isotopologue 12CD2NOH in the 300–3700 cm−1 region and its ν12 and ν9 bands: Vibrational and rovibrational analyses

The Fourier transform infrared (FTIR) spectrum of the formaldoxime isotopologue 12CD2NOH was recorded in the 500–3700 cm−1 region with a resolution of 0.50 cm−1 to identify its fundamental, overtone and combination bands and to measure their relative infrared (IR) band intensities. Furthermore, the high-resolution (0.00096 cm−1) FTIR spectrum of ν12 and ν9 bands of 12CD2NOH was recorded in Australian Synchrotron in the 300–510 cm−1 region for a rovibrational analysis. A total of 1060 IR transitions of the C-type ν12 band were fitted using the Watson's A-reduced Hamiltonian in the Ir representation with a root-mean-square (rms) deviation of 0.000524 cm−1. From the rovibrational analysis, the v12 = 1 state rovibrational constants up to all 5 quartic centrifugal distortion terms were derived for the first time. The band center of the ν12 band of 12CD2NOH was found to be 391.214740(46) cm−1. The ground state rovibrational constants up to all 5 quartic terms were determined for the first time by the fitting of 423 ground state combination differences (GSCDs) derived from the IR transitions of the ν12 band of 12CD2NOH of this work. The rms deviation of the GSCD fit was 0.000473 cm−1 using the Watson’s A-reduced Hamiltonian in the Ir representation. Furthermore, a total of 724 IR transitions of the predominantly B-type ν9 band of 12CD2NOH were fitted with a rms deviation of 0.000360 cm−1 to derive the band center at 465.151277(39) cm−1 and rovibrational constants of the v9 = 1 state up to 4 quartic terms for the first time. Additionally, all 3 rotational constants and 5 quartic centrifugal distortion terms of the ground state and 3 rotational constants of the v12 = 1 and v9 = 1 states of 12CD2NOH were computed from theoretical anharmonic calculations at 2 different levels of theory, B3LYP and MP2 with the cc-pVTZ basis set, for comparison with the experimental results. Close agreement was found for the calculated and experimental rotational constants of 12CD2NOH for the ground, v12 = 1 and v9 = 1 states. The vibrational frequencies (cm−1) of 12 fundamental bands of 12CD2NOH in the 300–3700 cm−1 region, and their IR band intensities (km/mol) were also calculated using B3LYP and MP2 with the cc-pVTZ basis set, and they were compared with the respective experimental data.

Fourier transform infrared (FTIR) spectrum (250–3800 cm−1) of formaldoxime-13C (13CH2NOH) and rovibrational analysis of its [formula omitted] band

The Fourier transform infrared (FTIR) spectrum of formaldoxime-13C (13CH2NOH) was recorded in the 600–3800 cm−1 region with a resolution of 0.50 cm−1 to identify its fundamental and overtone bands and to measure their relative infrared band intensities. Furthermore, the high-resolution (0.00096 cm−1) FTIR spectrum of the ν12 band of 13CH2NOH was recorded at the Australian Synchrotron in the 250–600 cm−1 region for a rovibrational analysis. A total of 1506 infrared (IR) transitions of the C-type ν12 band were fitted using the Watson's A-reduced and S-reduced Hamiltonians in the Ir representation with a root-mean-square (rms) deviation of 0.000364 cm−1 for both fits. From the rovibrational analysis, the v12 = 1 state rovibrational constants up to one sextic centrifugal distortion term were derived for the first time. The band center of the ν12 band of 13CH2NOH were found to be 397.365846(32) cm−1 in the A-reduced Hamiltonian. The ground state rovibrational constants up to one sextic term were improved with higher accuracy by fitting 1374 ground state combination differences (GSCDs) derived from the IR transitions of the ν8 and ν12 bands of 13CH2NOH, together with two previously reported microwave frequencies. Furthermore, a comparison of the experimental vibrational frequencies, IR band intensities, rovibrational constants (v12 = 1 and ground states) of 13CH2NOH and those derived from theoretical calculations at two levels of theory: B3LYP and MP2 with cc-pVTZ basis set were made. Close agreement was found for the calculated and experimental rovibrational constants of 13CH2NOH for both ground and v12 = 1 states.

Edging towards an understanding of CH/CH2 on nano-diamonds

Context. Nano-diamonds have been observed in only a handful of circumstellar regions 10–100 au from moderately bright stars (Teff ~ 8000–10 000 K). They have also been extracted from primitive meteorites; some of these are clearly pre-solar, that is to say that they formed far from the solar system and therefore traversed the interstellar medium, where they must exist but, because we see no evidence of them, must be extremely well hidden. Aims. Our goal is to understand if it is possible to constrain the sizes and shapes of nano-diamonds in circumstellar media using the observed ratio, [CH]/[CH2], of their surface CH2 and CH infrared bands at ≃3.43 μm and ≃3.53 μm, respectively. Methods. We calculated the CH and CH2 abundances on nano-diamonds using two approaches. The first assumes regular and semi-regular polyhedra (tetrahedra, octahedra, and cubes and their truncated forms). The second uses a diamond bonding network to derive the structures of tetrahedral and octahedral particles, and their truncated variants, and also of spherical nano-diamonds. Results. As a function of the particle size and shape, and for the two different calculation methods, we derived the relative abundance ratio [CH]/[CH2], which can then be weighted by their laboratory-measured infrared band intensities. The two methods give good agreement and indicate that the spread in values, over the different particle forms, is more that an order of magnitude for any size. Conclusions. We conclude that the ratio [CH]/[CH2], and their infrared band ratio, strongly depend upon particle size and shape. For a given shape or size, the ratio can vary by more than an order of magnitude. It may therefore be difficult to constrain nano-diamond sizes using the observed 3–4 μm spectra alone. James Webb Space Telescope mid-infrared spectra may help, but only if bands are size-specific.

Correlations Between Precursor Molecular Weight and Dynamic Mechanical Properties of Polyborosiloxane (PBS)

AbstractIt is possible to tailor the dynamic response of polyborosiloxanes (PBS) based on picking the right molecular weight of a precursor. The molecular weight of hydroxy‐terminated polydimethylsiloxane (PDMS) defines the shear‐stiffening performance of PBS due to straightforward condensation reaction between hydroxy end groups of PDMS and boric acid. Introduced borono groups behave as stickers, hence, are prone to supramolecular interactions. New correlations are discovered for five PBS synthesized from hydroxy‐terminated PDMS with different molecular weights. Si─O─B infrared band intensities for all PBS follow the same trend with molecular weight as the number of PDMS hydroxy groups which confirms the full completion of the reaction. After synthesis, the molecular weight of PBSs remained almost the same, which indicates the absence of significant chain scissoring, polymerization, or crosslinking. During the rheological analysis, it is found that crossover point modulus follows the same trend as the number of PDMS hydroxy groups and Si─O─B band intensities. PBS demonstrates a linear increase in peak forces with molecular weight during the drop weight impact test. The low molecular weight of a precursor, hence, a high number of stickers is a primary requirement for effective protection against low‐velocity impact.

Bifurcated Dihydrogen Bonding in the Uptake of Gas-Phase Diborane on Silica.

The interfacial chemistry of diborane (B2H6) with hydroxylated silica was investigated via in situ Fourier-transform infrared spectroscopy and temperature-programmed desorption. During exposure of silica to B2H6 under ultrahigh vacuum conditions, a decline in infrared band intensity assigned to excitation of the interfacial silanol O-H vibration at 3750 cm-1 and the associated appearance of a feature at 3687 cm-1 revealed hydrogen-bonding interactions between B2H6 and interfacial silanol groups. The IR spectrum for silica was completely recovered following desorption of the adsorbates, indicating that interactions between B2H6 and clean silica are reversible, in contrast to other reports on this system. During temperature-programmed desorption of diborane from silica, B2H6 was observed to desorb between 80 and 150 K, evidence for weak interactions between B2H6 and the surface. Electronic-structure calculations revealed that these interactions were due to bifurcated dihydrogen bonds between two terminal B-H groups of the adsorbate and interfacial silanol groups.

Infrared spectroscopy refines chronological assessment, depositional environment and pyrolysis conditions of archeological charcoals

Based on infrared spectral characteristics, six archeological sample sets of charcoals from German (5) and Brazilian (1) sites, covering the time span from the nineteenth century CE to 3950 BCE, were compared to a chronological (present to the fifteenth century BCE) series of Austrian charcoals. A typical chronological trend of several bands (stretch vibrations: O–C–O of carboxylates at 1,585–1,565 and 1,385–1,375 cm−1, C–O carboxylic acids at 1,260–1,250 cm−1) that indicate oxidation and subsequently increasing hydrophilicity (O–H stretch vibration at about 3,400 cm−1) was also contained in the archive samples. Three sample sets fit in the typical band development according to their age. For three sample sets this conformity was not observed. Despite the age of two sample sets (3950–2820 BCE), most charcoals were assigned to the Modern Period. Apart from the high degree of carbonization, anaerobic depositional conditions over a longer period of time seem to contribute to the surprising conservation. Non-removable mineral components in charcoals, as observed in a third sample set, strongly influence infrared band intensities and positions of organic compounds. The role of inorganic components in terms of charcoal aging, and the information we can obtain from spectral characteristics in an archeological context, are discussed.

Effects of micrometer-scale surface roughness on thermal infrared emittance spectra of silica glass

Surface roughness is known to decrease thermal infrared (TIR) absorption band intensity, but studies of the effect on geologically relevant samples are relatively limited. To determine the effect of surface roughness (with features smaller than ~2/3 of the wavelength) on TIR spectra, we investigated two glass compositions with prepared roughened surfaces: (1) high purity fused silica and (2) soda-lime glass (73 wt% SiO2). We roughened the surfaces of the glasses by sandblasting and polishing with grit paper. The surfaces were characterized with scanning electron microscopy and stylus profilometry. We then analyzed the roughened glasses with TIR emittance spectroscopy. Micrometer-scale roughness causes a decrease in TIR absorption band intensity, relative to a specular surface. No significant changes in band shape or shifts in wavelength were detected. As roughness increases, empirical results show a logarithmic decrease in TIR absorption band intensity. The logarithmic trends of the two glass compositions are different; empirical roughness calibrations do not translate across different compositions. A linear, least-squares spectral deconvolution using two endmembers, specular and blackbody, predicts model spectra of roughened glass surfaces with relatively low error. This is of consequence to orbital TIR measurements of poorly constrained targets, such as the martian surface, because micrometer-scale roughness is adequately modeled by the addition of a blackbody spectrum to the deconvolution endmember matrix.

Polarization effect in tip-enhanced infrared nanospectroscopy studies of the selective Y5 receptor antagonist Lu AA33810

A novel approach of combining conventional infrared spectroscopy (IR) and atomic force microscopy (AFM) is presented to better understand the behavior of a drug adsorbed on a metal substrate at the nanoscale level. Tip-enhanced infrared nanospectroscopy (TEIRA) was used for the first time to investigate Lu AA33810, a selective brain-penetrating Y5 receptor antagonist, after immobilization on gold nanoparticles (GNPs). Here, a gold coated AFM tip and gold substrate were used to obtain the near-field electromagnetic field trapping effect. Because of the huge signal enhancement, it was possible to obtain the spectral information regarding the self-assembled monolayer of the investigated molecule. The effect of two orthogonal polarizations (p- and s-polarization modulations) of the excitation laser beam on the spectral patterns is also discussed. The results show that there is a strong relationship between the state of polarization of the incident radiation and the relative infrared band intensities. Another factor affecting the observed spectral differences is the topology of the metal substrate, which may result in the induction of a cross-polarization effect. The performed analysis indicates that the C–C bond from the cyclohexyl group is oriented almost parallel to the metal surface. Conversely, the p- and s-polarized spectral variations suggest that the O=S=O angle is high enough to enable the simultaneous interaction of both oxygen atoms with the GNPs.

Investigation of OH bond energy for chemically treated alfa fibers

This work aims to study the hydrogen bond energy and distance for different samples of alfa fibers treated with thymol. The treatment duration and thymol concentration were varied and seem to have a great influence on infrared band intensities and positions. The number of hydrogen bonds is related to the infrared band intensity, whereas their energy and distance depend on the infrared band position.It was proven that the free hydroxyl groups are weakened and tend to disappear with fiber treatment. It is the same for intermolecular hydrogen bands between cellulosic chains that present a decrease in both intensity and frequency.The two intramolecular hydrogen bands increase in intensity but exhibit different behaviors regarding the calculated energy: while the band at 3268 cm−1 is weakened and shifted to higher wavenumbers, that at 3338 cm−1 keeps the same peak position and energy.

A new investigation of wax precipitation in Iranian crude oils: Experimental method based on FTIR spectroscopy and theoretical predictions using PC-SAFT model

Temperature dependency of infrared band intensity for methylene rocking vibration could be used as indication for creation of solid crystals while decreasing temperature. In this work, different experiments were conducted to measure wax appearance temperature, WAT, such as cross polarized microscopy, rheometry and FTIR spectroscopy. Three Iranian crude oils were characterized based on the SARA test and PC-SAFT model was developed to predict WAT. The obtained results by FTIR spectroscopy and PC-SAFT model were in quite agreement. FTIR spectroscopy determined higher WAT values which may be due to its higher sensitivity to smaller wax crystals. Also, the effect of a polymeric crystal modifier (EVA) and an aromatic solvent (toluene) on wax precipitation was investigated. EVA dramatically decreased the pour point of lower waxy crude oils. Toluene dissolved polar compounds such as asphaltene and consequently decreased WAT and pour point. This observation confirmed that asphaltene supports the wax crystallization and its growth.

Fourier‐transform infrared spectroscopic study of plasticization effects on the photodegradation of poly(fluorostyrene) isomers films

The photodegradation of poly(fluorostyrene) isomers with different amounts of phthalate and terephthalate plasticizers has been investigated with the aid of Fourier‐transform infrared spectroscopy. Photo irradiation was carried out with light from a Hydrogen‐Xenon lamp at 265 nm and 293 K. As irradiation time increased, changes occurred in the structure of the polymers due to the destruction of polymeric chains and the formation of new photo products during the degradation. The photo products caused shifts, an increase or decrease of the polymer vibrational frequencies, as well as changes in numerous infrared band intensities. The increase in the intensities of the analyzed ranges is attributed to the formation of carbonyl, hydroxyl, and aliphatic ketones and to the increase in the number of polyene structures that resulted from hydrogen abstraction during photodegradation reactions. The analysis of the Fourier‐transform infrared spectra of the irradiated and nonirradiated samples showed a noticeable formation of a new broad band centered at (1,727 cm−1, C=O), assigned to the growth of aliphatic ketones formerly from the reaction of reactive alkoxy radicals. Its intensity was found to increase with the increase in irradiation time and also with the increase in the amount of added terephthalate and phthalates plasticizer, indicating an increase in the efficiency of the photo degradation process. Trends of photostability of these isomers were found such that poly(para‐fluorostyrene) > poly(meta‐fluorostyrene) > poly(ortho‐fluorostyrene). The photodegradation process for these plasticized isomers was found to increase by the increase in the bulkiness of the plasticizer molecule. J. VINYL ADDIT. TECHNOL., 24:75–83, 2018. © 2015 Society of Plastics Engineers

Density Functional Theory on the Polymerization of Diaminofluorene

Density- functional theory (DFT) calculations on 2,7-diaminofluorene in order to understand the various possible mechanisms of growth, there are two possible mechanisms on it which involve the coupling of cationic radicals with another cationic radical or with a neutral oligomer. The electrochemical properties of this oligomer is understood, but until now there is very little known about the nature of the intermediates and the transition states leading to polymerization. The initial oxidation, forming stable intermediates, releasing protons and further oxidations are studied in terms of the charges distributions, energies changes in the geometry and vibrational frequencies have been calculated using DFT (B3LYP). Dramatic differences have been observed in the infrared band intensities of the cations compared to their neutral parents. Hydrogen bonding between DAF molecules in the crystal structure the direct comparison of theoretical calculations with experiment, so Hartree-Fock (HF) and Becke-Perdew density-functional theory (DFT) calculations are used as benchmarks for the semiempirical and molecular mechanics results.

Effect of γ irradiation on non-isothermal decomposition kinetics, X-ray diffraction pattern, infrared spectrum and antibacterial property of tris(1,2-diaminoethane)nickel(II)oxalate

Thermal decomposition, X-ray diffraction pattern, infrared (IR) spectrum and antibacterial property of tris(1,2-diaminoethane)nickel(II)oxalate were studied before and after γ-irradiation. Irradiation enhanced thermal decomposition. From X-ray diffraction studies, unirradiated and irradiated samples of the complex are found to be tetragonal. A change in lattice parameters was observed upon irradiation. Position and intensity of IR bands of –NH2 and >C=O group were found to be changed upon irradiation. Antibacterial studies showed that irradiation induced activity towards B. cereus.

High-resolution infrared spectra of vibrationally excited HC4H in a supersonic hydrocarbon plasma jet

High-resolution infrared spectra of diacetylene (HC4H) are recorded in the 3μm CH stretch region using continuous wave cavity ring-down spectroscopy (cw-CRDS). The HC4H molecules are generated in a pulsed and supersonic planar plasma expansion by discharging a C2H2/He/Ar gas mixture. The jet-cooling realizes a low rotational temperature of Trot∼17K. Vibrational temperatures are found to be relatively high, allowing the detection of vibrationally excited HC4H in direct absorption with energies up to 1800cm−1. In total, sixteen ro-vibrational bands are identified, where nine of them were not reported before. Detailed and systematic rotational analyses are presented, yielding spectroscopic parameters for a series of vibrational levels over energy regions of 0–1800 and 3300–5100cm−1. Using the observed infrared band intensities, two vibrational excitation temperatures of HC4H in the plasma jet, ∼570(50) K for the ν6, ν7 and ν8 bending vibrations, and ∼125(10) K for the ν9 bending vibration, are deduced.

Integrated Band Intensities of Ethylene (C212H4) by Fourier Transform Infrared Spectroscopy

The integrated band intensities of ethylene (12C2H4) in the 640–3260 cm−1 region were determined by Fourier transform infrared (FTIR) spectroscopy. The infrared absorbance spectra of the ν7 and ν10, ν12, ν7+ν8, ν6+ν10, v11, and ν9 and ν2+ν12 bands of ethylene recorded at a resolution of 0.5 cm−1 were measured at an ambient temperature of 296 K at various vapor pressures ranging from 3×10−5 to 1×10−3 atm to obtain respective Beer-Lambert's law plots. The measured integrated band intensities in cm−1/cm atm were S(ν9andν2+ν12)=112.20±0.24, S(ν11)=55.35±0.14, S(ν12)=41.22±0.30, and S(ν7andν10)=328.66±16.55. In addition, the measured infrared band intensities of the ν7+ν8 and ν6+ν10 combination bands of ethylene are reported for the first time: S(ν7+ν8)=21.701±0.028 cm−1/cm atm and S(ν6+ν10)=2.568±0.025 cm−1/cm atm.

The effect of metal binding on the characteristic infrared band intensities of ligands of biological interest

Abstract Since ∼40% of all proteins contain metal ions that perform a wide variety of functions indispensable for life processes, a plethora of experimental and theoretical methods have probed the interactions between metal ions and protein residues. Notably, previous studies have focused on how metal binding affects the protein ligands’ vibrational frequencies, but not the corresponding intensities (to the best of our knowledge), even though the latter are generally much more sensitive to structural and environmental alterations than the former. Hence, we have systematically evaluated how metal binding affects not only the protein ligands’ vibrational frequencies, but also the corresponding intensities and how these IR parameters depend on properties of the metal and its host ligand using density functional calculations. The results reveal that for a given protein ligand, the IR intensities, particularly those corresponding to bands without vibrational mode mixing, are quite sensitive to metal binding, and their changes are dictated by the metal’s charge-accepting ability and the ligand’s denticity. The results suggest that IR band intensities, along with vibrational frequencies, may be used to help interpret the IR spectra of protein binding sites in the metal-free and metal-bound states.

The infrared band intensities and other properties of the homodimers of the methyl and silyl halides: An ab initio study

Abstract The properties of the homodimers of methyl and silyl fluoride, chloride and bromide have been determined by means of ab initio molecular orbital calculations. The interaction energies, molecular structures, vibrational spectra and molecular orbital properties have been investigated, and some common features within each family have been observed. A number of systematic differences in the properties of the dimers have also been noted and rationalized. Typically, discussion of the results of such calculations has focused on the vibrational wavenumber shifts occurring on complexation, and the accompanying changes in the infrared band intensities have received relatively little attention. This paper aims to reposition infrared intensities as valid and useful parameters with which to interpret the formation of the homodimers of polar molecules.