Laser Raman Spectroscopy and Modelling of Diamondoids

We have been using our Renishaw Raman spectrometer to take Raman spectra of a number of diamondoid crystals, supplied to us by Molecular Diamond Technologies (a part of Chevron USA). We have also been performing ab initio DFT calculations to simulate these spectra, in order to assign the peaks to specific vibrational modes.

Diamondoids are hydrocarbon molecules that are totally or largely superimposable on the diamond lattice. The first in the series is adamantane, and higher diamondoids are made by fusing together successive adamantane units. A large number of such units makes diamond.

adamantane structurediamantane structure triamantane structurediamond structure

A crystal of neopentamantaneDiamondoids occur naturally in virtually all petroleum (1-10 ppm). Molecular Diamond Technologies extract them by reverse phase HPLC, and then recrystallise them by standard organic chemistry techniques. Samples are available for many of the smaller diamondoids, either as powders or as small crystals around 1 mm3 in size (see photo, right).

The Raman spectra of the diamondoids contain 2 regions of interest, a low energy region (400-1500 cm-1) due to stretching of the C-C cage, and a high energy region (2700-3100 cm-1) due to C-H stretches and bends. An example of one of the vibrations from each of these 2 regions can be seen below in the spectrum of 1212 pentamantane.

Raman spectrum of 1212 pentamantane
The Raman spectrum of 1212 pentamantane (above),
and an example of a C-C cage vibrational mode (below left) and a C-H stretching mode (below right)

One of the C-C modes in 1212 pentamantane One of the C-C modes in 1212 pentamantane

Raman Spectra

Some interactive spectra can be seen here, but spectra and structures for all of the diamondoids we have studied are below. The Raman spectra were taken from powder samples or single crystals using a 488 nm laser. The 3D structures of the molecules can be downloaded as mol files by clicking on the image. The Raman data can also be downloaded as an Excel file (x,y plot), or as an interactive JCamp spectrum (requires the Chime plug-in).

Name /
Structure		Raman SpectrumData
(Excel format)		Data
(JCamp format)
Adamantane
Adamantane		 Raman spectrum of adamantane ada.xls ada.jdx
Diamantane
Diamantane		 Raman spectrum of diamantane dia.xls dia.jdx
Triamantane
Triamantane		 Raman spectrum of triamantane tria.xls tria.jdx
[1(2)3] tetramantane
[1(2)3] tetramantane		 Raman spectrum of [1(2)3] tetramantane 1(2)3.xls 1(2)3.jdx
[121] tetramantane
[121] tetramantane		 Raman spectrum of [121] tetramantane 121.xls 121.jdx
[123] tetramantane
[123] tetramantane		 Raman spectrum of [123] tetramantane 123.xls 123.jdx
[1(2,3)4] pentamantane
[1(2,3)4] pentamantane		 Raman spectrum of [1(2,3)4] pentamantane 1(23)4.xls 1(23)4.jdx
[12(1)3] pentamantane
[12(1)3] pentamantane		 Raman spectrum of [12(1)3] pentamantane 12(1)3.xls 12(1)3.jdx
[12(3)4] pentamantane
[12(3)4] pentamantane		 Raman spectrum of [12(3)4] pentamantane 12(3)4.xls 12(3)4.jdx
[1212] pentamantane
[1212] pentamantane		 Raman spectrum of [1212] pentamantane 1212.xls 1212.jdx
[1213] pentamantane
[1213] pentamantane		 Raman spectrum of [1213] pentamantane 1213.xls 1213.jdx
[1234] pentamantane
[1234] pentmantane		 Raman spectrum of [1234] pentamantane 1234.xls 1234.jdx
3-methyl-[1(2,3)4] pentamantane
3-methyl-[1(2,3)4] pentamantane		 Raman spectrum of 3-methyl-[1(2,3)4] pentamantane methylpent.xls methylpent.jdx
[12312] hexamantane
[12312] hexamantane		 Raman spectrum of [12312] hexamantane 12312.xls 12312.jdx
[121321] heptamantane
[121321] heptamantane		 Raman spectrum of [121321] heptamantane 121321.xls 121321.jdx

References