Helium droplet calorimetry of strongly bound species: Carbon clusters from C2 to C12
Abstract
Helium droplet beam methods are a versatile technique that can be used to assemble a wide variety of atomic and molecular clusters. In recent years, methods have been developed to utilize helium droplets as nano-calorimeters to measure the binding energies of weakly bound complexes assembled within the droplet. In the current investigation we extend the helium droplet calorimetry approach to the study of a very strongly bound system: carbon clusters which are bound by several eV per atom. We utilize laser heating of bulk carbon samples to dope the helium droplets with evaporated carbon species. Depending on the laser target, the vaporization plume is found to consist primarily of C3 alone or C2 and C3. These species are sequentially captured by the droplet and assembled into larger carbon clusters in a stepwise manner. The assembled Cn clusters are detected via mass spectrometry of the doped droplets and the droplet sizes required to detect the various carbon clusters observed are used to estimate the reaction energies of the associated assembly pathways. The helium droplet data qualitatively reflect the trends in assembly energetics, but at first glance appear to yield energies that differ dramatically from theoretical values. Statistical modeling of the helium droplet calorimetry experiment reconciles the differences quantitatively. Our modeling also generates a calibration curve that relates the assembly/reaction energy and threshold mean droplet size over a range of energies from van der Waals interactions to chemical bonding, enabling helium droplet calorimetry methods to be applied quantitatively to a large number of systems.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Sep 01, 2014
- Source ID
- 10.1063/1.4895670
Entities
People
- Barbara A. Harruff-miller
- Christopher E. Bunker
- Michael A. Gord
- Peter Leatherman
- William K Lewis
Organizations
- Air Force Research Laboratory
- University of Dayton