Contribution of Graphene Molecules C$_{53}$ C$_{52}$ C$_{51}$ on Astronomical Diffuse Interstellar Bands (DIB)

Abstract

This molecular orbital analysis predicts that pure carbon graphene molecules would play an important role on astronomically observed Diffuse Interstellar Bands (DIB), rather than fullerene. Laboratory experiments precisely coincided with observed DIB bands as studied by E. Cambell et al., which were considered to originate from mono-cation fullerene-(C$_{60}$)$^{1+}$. To check theoretically a molecular orbital excitation of (C$_{60}$)$^{1+}$ was calculated by the Time-Dependent DFT. Calculated two bands were close to observed DIBs, but there were two problems, that the oscillator strength was zero, and that other three DIBs could not be reproduced. Laboratory experiments was the mass spectroscopic one filtering m/e=724, to suggest fullerene-(C$_{60}$)$^{1+}$ combined with He. However, there were other capabilities, as like He-atom intercalated 3D-graphite, [graphene(C$_{53}$)$^{1+}$--He--(C$_7$)], [graphene(C$_{51}$)$^{1+}$--He--(C$_9$)] and so on. A family of graphene (C$_{53}$), (C$_{52}$) and (C$_{51}$) was calculated. Results show that an astronomically observed 957.74nm band was reproduced well by calculated 957.74nm, also confirmed by laboratory experiment of 957.75nm. Other observed 963.26, 936.57 and 934.85nm bands were calculated to be 963.08, 935.89 and 933.72nm. Moreover, experimental 922.27nm band was calculated to be 922.02nm, which is not yet astronomically observed. Similarly, experimental 925.96, 912.80, 909.71 and 908.40nm bands were calculated to 926.01, 912.52, 910.32 and 908.55nm. It should be emphasized that graphene molecules may be ubiquitously floating in interstellar space.