"Prying open the black box – experimentally targeting critical intermediates from complex chemical networks," by Craig Taatjes (Sandia National Laboratories)

Date: 
Monday, May 16, 2016 - 11:00am to 12:00pm
Series: 
AMO Seminars

AMO Seminar

Physics and Astronomy Building (PAB) Room 4-330
Monday, May 16, 2016
11:00 AM

Guest Speaker: Craig Taatjes (Sandia National Laboratories)

Talk Title: "Prying open the black box – experimentally targeting critical intermediates from complex chemical networks"

Abstract:

The chemistry that occurs in combustion or in Earth’s atmosphere or in other complex chemically reacting systems is described at a basic level by an often unmanageably large web of interrelated chemical reactions. For some interesting targets – predicting the ignition of a fuel-air mixture, or predicting the formation of sulfate aerosols in the troposphere, for example – it turns out that the outcome may depend sensitively on a few reactions. An improvement in understanding of the fundamental chemistry of these reactions could therefore make a significant difference to predicting the effects of changing boundary conditions – new fuels for an engine, changes in anthropogenic emission to the atmosphere – on the performance of the chemical system. These critical reaction steps often involve chemical intermediate species that are difficult to investigate in isolation.

This talk describes our recent efforts to employ selective photoionization mass spectrometric methods for detection of gas-phase species to directly interrogate reactions of previously elusive types of chemical intermediates, highlighting two examples. First, the “Criegee intermediates” (carbonyl oxides) are zwitterionic molecules that are formed by the reaction of ozone with hydrocarbons, a process that is ubiquitous in Earth’s troposphere. The subsequent reactions of these molecules might play key roles in atmospheric chemistry cycles affecting regional air quality or global climate, but until our recent discovery of a method to produce this type of molecule efficiently (Science 335:204-7 (2012), 340:177-80 (2013)) no direct measurements of Criegee intermediate reactions had been possible. Second, a class of reactive radicals denoted “QOOH” (hydroperoxyalkyl radicals) are crucial intermediates that determine ignition properties of fuels and govern the formation of secondary organic aerosol in the atmosphere. Only one (especially stable) QOOH has ever been directly detected (Science 347:643-646 (2015)). I will describe what the new work on these ephemeral species may show about their reactivity, and discuss the relevance of fundamental chemical physics in modeling complex reacting systems.

This material is based upon work supported by the Division of Chemical Sciences, Geosciences and Biosciences, Office of Basic Energy Sciences (BES), United States Department of Energy (USDOE) and the Laboratory Directed Research and Development program of Sandia National Laboratories, a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the USDOE’s National Nuclear Security Administration under contract DEAC04-94AL85000.

Event Attachments: 
Location: 
PAB 4-330