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Occurrence and Isolation of Diamondoids from Natural Gas and Oil Reservoirs
Published in Sven Stauss, Kazuo Terashima, Diamondoids, 2017
Figure 5.3 displays the variation of the diamondoid content (adamantane, diamantane, and derivatives) as a function of EasyRo in percent. EasyRo (also written as EASY%Ro) is a model (Sweeney and Burnham, 1990) that allows predicting the level of vitrinitea maturation, that is the change in the level of vitrinite in a given sedimentary rock as a function of time and temperature. As can be seen in the figure, the maximum is reached at about 2.0 EasyRo.
Diamondoid geochemistry of Niger Delta source rocks: implication for petroleum exploration
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2020
Akinsehinwa Akinlua, Blessing I. Ibeachusim, Solomon A. Adekola, T.A. Adedosu, Yun Li, Yongqiang Q. Xiong
The ethyl adamantane and dimethyl diamantane geochemical parameters calculated for Wells AW, OP, GB, and OT samples are presented in Table 2. The ethyl adamantane index (EAI) and dimethyl diamantane index (DMDI-1) ranged from 78.18 to 91.46% and 66.25 to 70.52%, respectively in rock samples from Well AW (Table 2), which suggest mixed organic matter input. The EAI ratio values were not calculated for Wells OP, GB, and OT due to very low abundance of 1-ethyl adamantane (1-EA). However, the relatively high abundance of 2-ethyladamantane (2-EA) suggests terrestrial organic matter input to samples from Wells OP, GB, and OT. Also, the DMDI-1 values for some samples from Wells OP, GB, and OT were not calculated due to very low abundance of 3,4-dimethyl diamantane (3,4-DMD) and 4,9-dimethyl diamantane (4,9-DMD). The DMDI-1 ratio values for samples OP1, GB15, and OT2 indicates terrestrial organic matter input to the source rock.
Molecular dynamics simulation of the oscillatory behaviour and vibrational analysis of an adamantane molecule encapsulated in a single-walled carbon nanotube
Published in Philosophical Magazine, 2019
Yi Li, Zhen Yao, Bing-Bing Liu, Lin Wang, Cui Pei, Ye Yuan, Jing Ai
The tetracyclic cage structure, which consists of 10 carbon atoms, is the smallest repeating unit in a diamond crystal [1]. The corresponding hydrogen-terminated structure on the dangling carbon bond, which is called adamantane (C10H16), is the smallest diamondoid molecule (C4n+6H4n+12, where n = 1, 2, 3, etc.) [2]. The first three members in the series (adamantane, diamantane, and triamantane) possess single isomers, other members have different geometric isomerides [3]. Due to their outstanding chemical and physical properties, diamondoids have been considered useful for a variety of applications such as biomarkers for oil spill cleanup [4], electrochemical sensors [5], electronic emitters [6,7], and pharmaceutical chemicals [8]. In addition, functionalised diamondoids have been employed in the treatment of Alzheimer’s disease [9–11]. In fact, the high symmetry of the C10H16 molecule makes it an ideal candidate for studies of diamond-like materials [12,13]. Under ambient conditions, C10H16 has an ellipsoidal shape with major and minor radii (half the distance between two methylene carbons and half of the perpendicular line to this direction, respectively) of 1.719 and 1.554 Å, respectively [14,15]. While the bulk C10H16 crystal has a cubic phase with an Fm-3 m space group, at temperatures below 208 K or pressures above 0.5 GPa, the bulk C10H16 crystal transforms into a tetragonal phase with a P-421c space group [14,15].
Optical spectrum of the cyanoadamantane radical cation
Published in Molecular Physics, 2023
Parker B. Crandall, Viktoria D. Lovasz, Robert Radloff, Simone Stahl, Marko Förstel, Otto Dopfer
If diamondoids are present in interstellar regions, they likely also occur in their cationic state due to their low ionisation energies and the high flux of UV radiation and galactic cosmic rays [26]. Thus, laboratory spectra of the open-shell cations are required for astronomical detections. Only recently has the effort begun to measure electronic spectra of diamondoid cations. The cations of adamantane and diamantane (Ada+ and Dia+), the simplest diamondoids, were recently measured in the gas phase by electronic photodissociation spectroscopy (EPD) of cryogenic ions stored in an ion trap [27,28]. Despite cryogenic temperatures below 20 K, their spectra revealed unexpectedly broad spectral bands, with widths between 1 and 2 eV. In the case of Ada+, a vibrational progression attributed to the Jahn-Teller split D5/D6 doublet excited states was observed between 300 and 345 nm [27]. After excluding lifetime reduction contributions from fluorescence and collisions with background gas, an excited state lifetime of ∼30 fs was extracted from the widths of the peaks. The large width of the Ada+ transitions arising from short lifetime was recently confirmed by spectroscopy in helium nanodroplets at 0.4 K [29]. For Dia+, no vibronic features were resolved in its EPD spectrum [28]. To determine the extent of lifetime broadening, time-dependent density functional theory (TD-DFT) calculations were employed to optimise the geometry of the observed D5 excited state followed by a Franck-Condon (FC) simulation. By convoluting the spectrum with different widths, it was determined that a lifetime below ∼20 fs closely resembles the experimental band contour. Thus, it has been reasoned that the excited states for Ada+ and Dia+ below 6 eV undergo ultrafast relaxation, either by internal conversion to highly excited vibrational states of the electronic D0 ground state or by predissociation [27,28]. Combined with FC congestion arising from excitation of unresolved, close-lying vibrational modes, such short lifetimes produce exceptionally broad absorption spectra. If higher-order diamondoids exhibit the same behaviour, this would eliminate all bare diamondoid cations as potential carriers of the DIBs. However, electronic spectra for cations larger than Dia+ still need to be measured.