The thermal rate coefficients and kinetic isotope effects have been calculated using ring polymer molecular dynamics (RPMD) for the prototypical reactions between methane and several hydrogen isotopes (H, D, and Mu). The excellent agreement with the theoretical rate coefficients of the H + CH 4 reaction obtained previously from a multiconfiguration time-dependent Hartree (MCTDH) calculation on the same potential energy surface provides strong evidence for the accuracy of the RPMD approach. These quantum mechanical rate coefficients are also in good agreement with the results obtained previously using the transition-state theory with semi-classical tunneling corrections for the H/D + CH 4 reaction reactions. However, it is shown that the RPMD rate coefficients for the ultralight Mu reaction with CH 4 are significantly smaller than the experimental data, presumably suggesting inaccuracies in the potential energy surface.Significant discrepancies between the RPMD and transition-state theory results have also been found for this challenging system.
The photoluminescence (PL) of multiwalled carbon nanotubes (MWCNTs) synthesized with ethanol flames
was investigated at temperatures from 30 to 300 K. Broad-band PL emission in the near-infrared region was
observed at temperatures below 240 K. The PL intensity was abruptly boosted up at 240 K, and then quickly
became quenched and undetectable as the temperature was further increased. The PL emission of the MWCNTs
only appeared in the first cycle of the temperature rising. However, it could be recovered by exposing the
sample in an oxygen-abundant environment. We propose that the PL emission of the MWCNTs is resulted
from the carbon oxyhydride-like fluorophors bound to the MWCNTs surface.
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