We present a comprehensive study of the chiral-index assignment of carbon nanotubes in aqueous suspensions by resonant Raman scattering of the radial breathing mode. We determine the energies of the first optical transition in metallic tubes and of the second optical transition in semiconducting tubes for more than 50 chiral indices. The assignment is unique and does not depend on empirical parameters. The systematics of the socalled branches in the Kataura plot are discussed; many properties of the tubes are similar for members of the same branch. We show how the radial breathing modes observed in a single Raman spectrum can be easily assigned based on these systematics. In addition, empirical fits provide the energies and radial breathing modes for all metallic and semiconducting nanotubes with diameters between 0.6 and 1.5 nm. We discuss the relation between the frequency of the radial breathing mode and tube diameter. Finally, from the Raman intensities we obtain information on the electron-phonon coupling.

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From resonant Raman scattering on isolated nanotubes we obtained the optical transition energies, the radial breathing mode frequency and Raman intensity of both metallic and semiconducting tubes. We unambiguously assigned the chiral index (n1, n2) of ≈ 50 nanotubes based solely on a third-neighbor tight-binding Kataura plot and find ωRBM = (214.4±2) cm −1 nm/d+(18.7±2) cm −1 . In contrast to luminescence experiments we observe all chiralities including zig-zag tubes. The Raman intensities have a systematic chiral-angle dependence confirming recent ab-initio calculations.PACS numbers: 78.67. Ch, 78.30.Na The successful preparation of single-walled carbon nanotubes in solution where the tubes are prevented from rebundling has opened a new direction in carbon nanotube research [1,2,3,4]. Strong luminescence by direct recombination from the band gap was detected in these isolated tubes, whereas in nanotube bundles no luminescence is observed. The electronic structure of carbon nanotubes and the optical transition energies vary strongly with their chiral index (n 1 , n 2 ) [5]. Because the synthesis of nanotubes with a predefined chiral index has not been achieved so far, luminescence experiments were carried out on tube ensembles with unknown composition of chiral angles. Several attempts to assign the chiral index (n 1 , n 2 ) to the experimentally observed luminescence peaks were reported [2,4,6,7]. With a unique assignment, one could validate and possibly revise theoretical models of the electronic band structure. Moreover, such an assignment would allow to characterize the tubes after their production and to control their separation [8].Bachilo et al. suggested an (n 1 , n 2 ) assignment of the first and second transition energies in semiconducting tubes [2]. Their assignment is based on pattern recognition between experiment and theory in a plot of the second transition (excitation energy) versus the first transition (emission energy) [9]. The patterns, however, were not unique, and the frequency of the radial breathing mode (RBM) was used to find an anchoring element that singles out one of the assignments. Surprisingly, zig-zag tubes were not detected in these luminescence experiments. Bachilo et al. concluded that the concentration of tubes with chiral angles close to the zig-zag direction was very low in the sample [2].The electronic transition energies of metallic nanotubes cannot be detected by luminescence experiments. An elegant approach is to record Raman resonance profiles [10,11,12,13], with maximum intensity close to the real transitions in the electronic band structure. Resonance profiles from nanotubes in solution were first reported by Strano et al. [14]; their (n 1 , n 2 ) assignment to the transition energies was based on the RBM frequency to tube diameter relationship of Ref. [2]. The resonance profiles of the so-assigned RBM peaks were then used to find an empirical expression for the transition energies in metallic tubes.In this paper we present the transition energies of both metallic a...

We show by ab initio calculations that the electron-phonon coupling matrix element M e-ph of the radial breathing mode in single-walled carbon nanotubes depends strongly on tube chirality. For nanotubes of the same diameter the coupling strength |M e-ph | 2 is up to one order of magnitude stronger for zig-zag than for armchair tubes. For (n1,n2) tubes M e-ph depends on the value of (n1 − n2) mod 3, which allows to discriminate semiconducting nanotubes with similar diameter by their Raman scattering intensity. We show measured resonance Raman profiles of the radial breathing mode which support our theoretical predictions.

An enhanced aerosol layer near the tropopause over Asia during the June-September period of the Asian summer monsoon (ASM) was recently identified using satellite observations. Its sources and climate impact are presently not well-characterized. To improve understanding of this phenomenon, we made in situ aerosol measurements during summer 2015 from Kunming, China, then followed with a modeling study to assess the global significance. The in situ measurements revealed a robust enhancement in aerosol concentration that extended up to 2 km above the tropopause. A climate model simulation demonstrates that the abundant anthropogenic aerosol precursor emissions from Asia coupled with rapid vertical transport associated with monsoon convection leads to significant particle formation in the upper troposphere within the ASM anticyclone. These particles subsequently spread throughout the entire Northern Hemispheric (NH) lower stratosphere and contribute significantly (∼15%) to the NH stratospheric column aerosol surface area on an annual basis. This contribution is comparable to that from the sum of small volcanic eruptions in the period between 2000 and 2015. Although the ASM contribution is smaller than that from tropical upwelling (∼35%), we find that this region is about three times as efficient per unit area and time in populating the NH stratosphere with aerosol. With a substantial amount of organic and sulfur emissions in Asia, the ASM anticyclone serves as an efficient smokestack venting aerosols to the upper troposphere and lower stratosphere. As economic growth continues in Asia, the relative importance of Asian emissions to stratospheric aerosol is likely to increase.