Matrix Raman spectra of the molecular halogens: Resonance Raman spectra of isolated and aggregated I2

Abstract Iodine vapor was suspended in Ar, Kr, Xe and N 2 matrices at 16K using several dilutions (Ar/I 2 =400/1, 1000/1, 2500/1) and the Raman spectra were studied using krypton and argon plasma exciting lines. Two progressions were observed in the Ar/I 2 =400 samples: a weak one beginning at 212±1 cm −1 , which has the gas‐phase I 2 spacing, and extending out to 11ν using 5145 Å excitation, and a very strong series beginning at 180 ± 1 cm −1 and extending out to 11ν with vibrational intervals near solid I 2 values. The two progressions exhibited comparable intensities in the Ar/I 2 =1000 experiment. In the Ar/I 2 =2500 experiments, the gas‐phase‐like series was intense and the 180 cm −1 interval spectrum was absent. The very strong I 2 fundamental and regular overtone progressions increased in length and in intensity as the exciting wavelength decreased 6471 to 5145 Å, reaching the absorption band maximum, and then decreased in length and intensity using 4880 and 4579 Å excitation. These observations are characteristic of resonance Raman spectra.