Infrared Spectrum and Dipole—Dipole Coupling in Crystalline Cyanogen

Abstract

The infrared spectrum of a polycrystalIine film of cyanogen at 80 0 K is reported for the region from 4000 to 500 em-I. In an attempt to account for the splitting observed for the 1'3 fundamental, transition-dipoletransition-dipole interactions have been calculated by computing lattice sums for a variety of crystal shapes and sizes. It is concluded that dipole-dipole coupling can account for only a fraction of the observed splitting.

Infrared Spectra and Vapor Pressures of Crystalline C2N2, with Comparisons to Crystalline HCN

“…Verderame et al (1963) also show the same two features that we found for the band near 2165 cm −1 , and with the same separation within those authors' stated uncertainty of 0.5 cm −1 with a dispersive spectrometer. We also observed weak isotopic features (e.g., 2148 cm −1 for 15 NCCN and 2139 cm −1 for NC 13 CN) reported by Verderame et al (1963). With our highest resolution, 0.125 cm −1 , we were just able to discern an additional splitting in the ν 3 peak of Figure 2, confirming the small splitting reported by Verderame & Nixon (1965), apparently for the first time.…”

“…Those authors, and later Ospina et al (1988) and Dello Russo & Khanna (1996), published IR spectra of crystalline C 2 N 2 , but on such small scales that direct visual comparisons are difficult. Qualitatively, our spectrum of crystalline C 2 N 2 resembles that of Verderame et al (1963) at 80 K. Peak positions in those same authors' Table 1 are within about 1 cm −1 of our own and clearly indicate a small side peak for each of the three large bands of our Figure 2. Verderame et al (1963) also show the same two features that we found for the band near 2165 cm −1 , and with the same separation within those authors' stated uncertainty of 0.5 cm −1 with a dispersive spectrometer.…”

“…Qualitatively, our spectrum of crystalline C 2 N 2 resembles that of Verderame et al (1963) at 80 K. Peak positions in those same authors' Table 1 are within about 1 cm −1 of our own and clearly indicate a small side peak for each of the three large bands of our Figure 2. Verderame et al (1963) also show the same two features that we found for the band near 2165 cm −1 , and with the same separation within those authors' stated uncertainty of 0.5 cm −1 with a dispersive spectrometer. We also observed weak isotopic features (e.g., 2148 cm −1 for 15 NCCN and 2139 cm −1 for NC 13 CN) reported by Verderame et al (1963).…”

“…The spectrum of crystalline C 2 N 2 ice at 100 K is shown in Figure 2, with the three labeled transitions being the strongest bands from 5000 to 300 cm −1 , and the main cyanogen features examined for this study. Each of the three bands of Figure 2 consists of a small and large component, as expected from the theory of vibrations in crystalline solids (e.g., Verderame et al 1963). As for intensities, even a casual comparison of the ice thicknesses and peak heights in Figures 1 and 2 shows that C 2 N 2 is a particularly weak IR absorber compared to HCN.…”

“…As with the n 670 and ρ of crystalline HCN, that iceʼs IR spectrum was discussed by Gerakines et al (2022), so here we focus on C 2 N 2 . The weakness of cyanogenʼs mid-IR features already has been mentioned, an observation made earlier by Verderame et al (1963). Those authors, and later Ospina et al (1988) and Dello Russo & Khanna (1996), published IR spectra of crystalline C 2 N 2 , but on such small scales that direct visual comparisons are difficult.…”