Fourier transform infrared studies of the N2–O2 binary system

Abstract

Solid solutions (N 2) x (O 2) 1-x have been investigated by infrared absorption measurements mainly in the O 2 and N 2 stretching regions, between 60-10 K, completing former similar studies by Raman scattering. We produced thermodynamically stable samples by a careful thermal treatment, followed by cooling/heating cycles over weeks, during which we took spectra. From fingerprints in infrared spectra we deduce phase transition lines, solubility lines and suggest a refined, improved T-x% phase diagram with respect to inconsistencies between those in literature. Spectra of N 2-O 2 mixtures are pretty complex but referring to known spectra of pure systems N 2 or O 2 we were able to assign and interpret broad (~100 cm-1) phonon side bands to fundamentals and electronic transition (O 2) depending on actual temperature and concentration. Narrow features in spectra (<10 cm-1) were attributed to the vibron DOS of N 2 or O 2 , whose bandwidth, band shape and intensity are different and characteristic for each phase. Differences between pure and mixed systems were pointed out. Matrix isolation technique (2 ppm of CO) was used to probe our mixture.

From optical spectra to phase diagrams—the binary mixture N2–CO

“…The phase coexistence region (hcp and cubic) of low temperature phases is more narrow in our case; as well the solidus-liquid range, i.e. that our methodfrom changes in optical spectra to phase diagrams -is working and can be applied to the other phase diagrams like pressure/concentration for N 2 -O 2 [9] or N 2 -CH 4 (in progress); we already finished similar studies at high pressure (p < 10 GPa) and low temperatures (T < 300 K) of pure CO and N 2 -CO mixtures [18].…”

“…2 in [8]). In FTIR studies about N 2 -O 2 mixtures [9], which are IR inactive, we determined the actual concentration by means of chromatography and mass-spectrometry; after measurements the sample was evaporated into a test volume and was then analyzed. Here we determined the actual concentration via relative intensities I pure and I mix of IR spectra of the (0-2) and (0-3) CO vibration of pure CO in comparison to a mixture of N 2 -CO (Fig.…”

“…10, which is showing spectra of the n 3 -CO 2 mode and n 0 -N 2 in mixture during cooling/heating cycle; even little details of the IR bands are conserved. In general due to experiences with the binary mixture N 2 -O 2 [9] we relay more on the second cycle -the warming cycle, because in that case we have thermodynamically stable samples which we proved by spectroscopy (e.g. homogeneous bandwidth); in the first cooling down of the sample overcooling effects may occur which shift phase transitions.…”

“…The vibron density of states (DOS) is modelled by standard lattice dynamics; only vibron excitations at wave vector k = 0 are known from Raman scattering (see Fig. 22 in [9]). Some details of the shape of the vibron DOS can be deduced from the two-vibron spectra in a-N 2 ; this is a combinational excitation of (0-1) in one molecule and (0-1) in a neighbouring molecule (Fig.…”

A New Two-molecule Combination Band as a Diagnostic of Carbon Monoxide Diluted in Nitrogen Ice on Triton

“…For example, see Ida et al (2010) and Tajti et al (2017). Previous identifications of twomolecule combination bands in spectra of ice samples include single photons exciting the fundamental mode of adjacent N 2 molecules (Grundy et al 1993) and adjacent N 2 and O 2 molecules (Minenko & Jodl 2006) as well as single photons exciting an electronic tran- Figure 1. The harmonic oscillator potential (red line) and more realistic Morse potential (black line) for vibration of a generic diatomic molecule.…”