A vibrational assignment of adamantane and some of its isotopomers. Empirical versus scaled semiempirical force field

Rotationally resolved infrared spectroscopy of adamantane

“…Since these modes are IR inactive, experimental frequencies for these modes have been obtained by Raman spectroscopy of adamantane in condensed-phase samples. 14,16 When strong Coriolis interaction occurs, the perturbing mode may become weakly active, but we did not detect any absorption in the region of ν 12 or ν 19 . Since no large perturbations were detected in the branches of ν 30 , it was treated as an isolated band in the analysis.…”

“…structure, we clearly distinguish the presence of one or several other Q-branches belonging to hot bands. Since the spectra have been recorded at room temperature, the hot bands may involve several quanta of the low frequency modes centered at 355 cm −1 (ν 19 mode, F 1 symmetry), 16 400 cm −1 (ν 12 mode, E symmetry), 14 and 442 cm −1 (ν 30 mode, F 2 symmetry). The fit of the fundamental band included 3530 lines yielding 13 parameters of the Hamiltonian described in Sec.…”

“…This effect may be due to a local perturbation. The ν 5 mode located at 758 cm −1 having A 1 symmetry 14 cannot be responsible for the splitting of the A, E, F species through Coriolis interaction, but might be responsible for a perturbation in the energy spacing (the F − 2 levels being more perturbed than the F + 2 ). The reader is refered to Fig.…”

“…The nearest vibrational levels which may cause Coriolis interaction with ν 28 include ν 18 (calculated at 887 cm −1 with F 1 symmetry) 16 and ν 11 (calculated at 917 cm −1 with E symmetry). 16 Experimentally, the position of ν 11 is known from Raman spectra: 14 953 cm −1 in solution and 950 cm −1 in a powder sample. In the next paragraph, we propose to assign to ν 11 a band located at 949.42 cm −1 in our gas phase spectrum.…”

“…Vibrational spectra are available for adamantane, [14][15][16] various larger diamondoid molecules 17 including some of their positively charged ions 18,19 and diamond nanoparticles. 4,20 Adamantane displays strong Raman activity and Raman spectra of adamantane 16 as well as of several larger diamondoid molecules 21,22 have been reported.…”