Infrared Spectra of Carbon Monoxide in an Argon Matrix

Abstract

The infrared absorption spectrum of carbon monoxide in an argon matrix shows prominent bands at 2148.8 and 2138.0 cm—1 with half-widths, respectively, 1.5 cm—1 and 3.5 cm—1. The relative intensities of these bands are extremely dependent upon a variety of experimental conditions, including sample concentration, window temperature, and deposition rates. The variability shows that CO isolated in argon absorbs at 2148.8 cm—1 and that it does not rotate. The lower frequency absorption is due to aggregates. The frequency shift of the argon-isolated CO absorption relative to that of gaseous CO shows that carbon monoxide fits tightly in the argon lattice. In contrast, the CO aggregates absorb at lower frequency than gaseous carbon monoxide. Isotopic studies using 13C16O reveal vibrational coupling of 1.1 cm—1 between isotopically identical molecules in an aggregate. An increase in matrix cavity diameter would be needed if a stationary CO molecule begins to rotate in argon. This ``site expansion,'' which could be as much as 0.4 Å, may be an important factor inhibiting rotation.

The CO stretch frequency of fully CO covered Ag-clusters in dependence on cluster size

“…2 , were prepared in the gas phase and isolated in a CO matrix while the distribution with the mean size n"30 atoms/cluster (-· -) was produced by the aggregation of atoms during matrix growth of an Ar(99%)/CO(1%) mixture. The matrices were prepared at 25 K and the amount of the condensed metal measured with a micro-balance was about 600 A s /cm vibrational frequency of the CO monomer isolated in Ar is 2138 cm\ [17]. A weak feature at 2090 cm\ resulting from small amounts of the isotopic species CO and CO is removed from the spectra for the sake of clarity.…”

FTIR study of carbonate loss from carbonated apatites in the wide temperature range

“…This behavior suggests the attribu- tion of the band at 2138.2 cm Ϫ1 to an aggregate of CO obviously favoured at lower M/A ratio in agreement with previous proposals. 23,25 In this work, however, the identification of the bands has less significance than the total amount of CO produced by the samples during vaporization. The calculated area of the CO band versus vaporization temperature is shown in Figure 3.…”

Librational motion of CO in solid Ar: Raman and IR spectra and quantum simulations

“…The study of vibrational and rotational degrees of freedom of CO molecule in crystalline solids has been quite comprehensive, and a recent, vast collection of spectroscopic studies and explaining theories was compiled by Fajardo et al [3] In particular, the solid argon case has received considerable attention [4][5][6][7][8][9][10][11][12][13][14][15][16][17]. (For the gas phase Raman case, see Thibault et al [18].)…”

“…The debate over the assignment of the observed transition bands lasted over three decades. Although the main focus was on the question whether some of the spectral bands should be assigned to CO monomer or dimer, some earliest studies [6,7,11] suggested that there were no rotational motion at all. Latest studies [15][16][17] concluded, in agreement with most of the previous results [5,[8][9][10], that the observed IR spectrum indeed shows signs of rotations based on the reversible temperature dependence of the band widths.…”