Optical Spectrum of the Adamantane Radical Cation

Abstract

Known for their stable structural and thermal properties, diamondoids and their radical cations are viable candidates as carriers for diffuse interstellar bands. 1 While previous diamondoid research has mainly focused on neutral molecules and their derivatives, little is known about their radical cations, which may form in interstellar environments by ionizing radiation. 2 We report the first experimental optical spectrum of the simplest diamondoid cation, the adamantane radical cation (C 10 H 16 + ), obtained via electronic photodissociation spectroscopy at 5 K between 310-1000 nm. The optical spectrum reveals a broad peak between 420-850 nm, assigned to the D 2 ( 2 E) ← D 0 ( 2 A 1 ) transition. This feature exhibits no vibrational structure, despite an experimental temperature below 20 K, due to lifetime broadening and/or Franck-Condon congestion. A second band system originating at 345 nm does reveal a vibrational progression and is attributed to the overlapping D 5 ( 2 A 1 )/D 6 ( 2 E) ← D 0 ( 2 A 1 ) transitions split by the Jahn-Teller effect. Comparison of the spectrum with known diffuse interstellar bands suggests that C 10 H 16 + is not likely to be a carrier. However, the strong absorption features in the UV to near IR show promise in the investigation of higher order diamondoid cations as potential candidates. 3

Opening of the Diamondoid Cage upon Ionization Probed by Infrared Spectra of the Amantadine Cation Solvated by Ar, N2, and H2O

“…IRPD spectra of Ada + L cluster ions (L=He, N 2 , H 2 O) indicate Jahn‐Teller distortion and C−H bond activation upon ionization into the cation ground state [19g,20] . Significantly, all transitions observed could be assigned to cluster isomers composed of the nascent cage structure of Ada + , consistent with low‐resolution EPD spectra of bare Ada + generated by electron ionization (EI) [5b] . Due to vertical ionization given by the Franck‐Condon principle, photoelectron and photoionization spectra of Ada only probe the vibronic structure of the nascent cation geometry and thus detect solely the canonical cage structure of Ada + [3l,19b,l,m,o] .…”

“…Compared to Ama + , considerably more information is available for the Ada + parent cation, which has been characterized by photoelectron, photoionization, and fragmentation spectroscopy, IR and electronic photodissociation (IRPD, EPD) spectroscopy, and quantum chemical calculations [3l,5b,19] . IRPD spectra of Ada + L cluster ions (L=He, N 2 , H 2 O) indicate Jahn‐Teller distortion and C−H bond activation upon ionization into the cation ground state [19g,20] .…”

Microsolvation of H2O+, H3O+, and CH3OH2+ by He in a cryogenic ion trap: structure of solvation shells

“…The cluster growth experiments are carried out in an ion-trap quadrupole/time-of-flight tandem mass spectrometer (BerlinTrap) described in detail elsewhere. 68,73 Briefly, it consists of an ion source for ion generation, a quadrupole mass spectrometer (QPMS) for ion selection, an electrostatic bender for ion deflection, an octupole ion guide for transferring the ions into a cryogenic 22-pole ion trap used for trapping and cooling the ions via He buffer gas (purity 5.0, Air Liquide, impurities O 2 and H 2 O < 3 ppm), an Einzel lens stack for focusing the ions, and finally a reflectron time-of-flight (ReTOF) mass spectrometer for detecting the product ions. For the current study, the original electrospray ionization (ESI) source is used to produce the closed-shell ions H 3 O + , CH 3 + , and CH 3 OH 2 + , 68 while for the open-shell H 2 O + ions the ESI source is replaced by an electron ionization (EI) source.…”

“…For the current study, the original electrospray ionization (ESI) source is used to produce the closed-shell ions H 3 O + , CH 3 + , and CH 3 OH 2 + , 68 while for the open-shell H 2 O + ions the ESI source is replaced by an electron ionization (EI) source. 73 H 3 O + and CH 3 OH 2 + are readily produced by ESI of solutions containing H 2 O or CH 3 OH with some addition of acetic acid. CH 3 + is a major fragment of CH 3 OH 2 + by elimination of H 2 O.…”

Electronic spectroscopy of cationic adamantane clusters and dehydrogenated adamantane in helium droplets

“…[1][2][3][4] Due to its structure, adamantane shows unique thermal stability and has become a popular hydrocarbon for a wide range of applications such as material and polymer science, molecular electronics, biomedical sciences, and chemical synthesis. [5][6][7][8][9] Diamondoids are also expected as viable candidates as carriers for diffuse interstellar bands (DIBs), [10][11][12][13][14][15][16][17] as their structural and thermal stability make them more able to withstand the harsher conditions in interstellar environments. As such, spectroscopic signatures of such compounds are required to compare with astronomical observations.…”