2nd October 2012, Belfast, UK: Despite its low atmospheric concentration and comical connections, nitrous oxide is no laughing matter. It is the fourth largest contributor to global warming, behind water vapour, carbon dioxide and methane, and has replaced CFCs as the dominant ozone-depleting substance emitted by humans - a situation that is unlikely to change throughout the 21st Century.
Stratospheric ozone is regulated by nitric oxide, formed when nitrous oxide reacts with oxygen atoms. However, even though extensive experimental studies into this reaction have been conducted, the photodissociation mechanism of nitrous oxide, the kinetic energy and internal state distributions of fragments, and the angular distributions of fragment ions are still unclear.
Now, a team working at China's National Synchrotron Radiation Laboratory at Hefei has used a novel threshold photoelectron-photoion coincidence (TPEPICO) velocity imaging technique to determine the formation pathways of nitric oxide. The corresponding vibrational state distributions of NO+ have also been identified for every dissociation channel.
"Ultra low noise performance is vital in our work on the photodissociation dynamics of ions," says one of the lead researchers, Xiaoguo Zhou. "At the heart of the experimental apparatus is Andor's thermoelectrically cooled iKon-M 934 camera. Compared to cameras normally used in ion imaging experiments, the Andor camera offered very much lower read noise and high sensitivity over accumulation periods of up to 60 minutes. We also used the Andor Solis software supplied with the camera to process the images. For instance, we would often need to subtract the background and Solis processed the images easily and quickly."
The TPEPICO apparatus was set up at the synchrotron's U14-A beam line and a continuous supersonic molecular beam of pure N2O gas introduced into the photoionization region through a homemade 30 micron diameter nozzle. Photoelectrons and photoions were collected through a special ion lens to map their velocity images simultaneously and the coincident photoions projected onto a dual microchannel plate backed by a phosphor screen where the Andor DU934N-BV TE-cooled CCD detector recorded the images. By applying a pulsed high voltage on MCP as the mass gate, the three-dimensional (3D) time-sliced image of ions was obtained.
Andor's iKon-M 934 series cameras are designed to offer the ultimate in high sensitivity, low noise performance, which makes them ideal for demanding imaging applications. Boasting up to 95% QEmax, high dynamic range, 13µm pixels and exceptionally low readout noise, these high resolution CCD cameras benefit from negligible dark current with industry-leading thermoelectric cooling down to -100°C. To learn more about the iKon-M series, please visit the Andor website [http://www.andor.com].
The 2 images above are available for download. Either click on the image or contact John Waite at Catalyst Communications.
1. Xiaofeng Tang, Mingli Niu, Xiaoguo Zhou, Shilin Liu, Fuyi Liu, Xiaobin Shan and Liusi Sheng "NO+ formation pathways in dissociation of N2O+ ions at the C2S+ state revealed from threshold photoelectron-photoion coincidence velocity imaging," The Journal of Chemical Physics, 134, 054312 (2011)
Andor is a world leader in Scientific Imaging, Spectroscopy Solutions and Microscopy Systems. Established in 1989 from Queen's University in Belfast, Northern Ireland, Andor Technology now employs over 300 people in 16 offices worldwide, distributing its portfolio of over 70 products to 10,000 customers in 55 countries.
Andor’s digital cameras, designed and manufactured using pioneering techniques developed in-house, allow scientists around the world to measure light down to a single photon and capture events occurring within 1 billionth of a second. This unique capability is helping them push back the boundaries of knowledge in fields as diverse as drug discovery, toxicology analysis, medical diagnosis, food quality testing and solar energy research. More information about Andor Technology PLC (LSE: AND) is available at the company's website [www.andor.com].
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