Nav: Home

The inner lives of molecules

April 04, 2017

WASHINGTON, D.C., April 4, 2017 -- Quantum mechanics rules. It dictates how particles and forces interact, and thus how atoms and molecules work -- for example, what happens when a molecule goes from a higher-energy state to a lower-energy one. But beyond the simplest molecules, the details become very complex.

"Quantum mechanics describes how all this stuff works," said Paul Hockett of the National Research Council of Canada. "But as soon as you go beyond the two-body problem, you can't solve the equations." So, physicists must rely on computer simulations and experiments.

Now, he and an international team of researchers from Canada, the U.K. and Germany have developed a new experimental technique to take 3-D images of molecules in action. This tool, he said, can help scientists better understand the quantum mechanics underlying bigger and more complex molecules.

The new method, described in The Journal of Chemical Physics, from AIP Publishing, combines two technologies. The first is a camera developed at Oxford University, called the Pixel-Imaging Mass Spectrometry (PImMS) camera. The second is a femtosecond vacuum ultraviolet light source built at the NRC femtolabs in Ottawa.

Mass spectrometry is a method used to identify unknown compounds and to probe the structure of molecules. In most types of mass spectrometry, a molecule is fragmented into atoms and smaller molecules that are then separated by molecular weight. In time-of-flight mass spectrometry, for example, an electric field accelerates the fragmented molecule. The speed of those fragments depends on their mass and charge, so to weigh them, you measure how long it takes for them to hit the detector.

Most conventional imaging detectors, however, can't discern exactly when one particular particle hits. To measure timing, researchers must use methods that effectively act as shutters, which let particles through over a short time period. Knowing when the shutter is open gives the time-of-flight information. But this method can only measure particles of the same mass, corresponding to the short time the shutter is open.

The PImMS camera, on the other hand, can measure particles of multiple masses all at once. Each pixel of the camera's detector can time when a particle strikes it. That timing information produces a three-dimensional map of the particles' velocities, providing a detailed 3-D image of the fragmentation pattern of the molecule.

To probe molecules, the researchers used this camera with a femtosecond vacuum ultraviolet laser. A laser pulse excites the molecule into a higher-energy state, and just as the molecule starts its quantum mechanical evolution -- after a few dozen femtoseconds --another pulse is fired. The molecule absorbs a single photon, a process that causes it to fall apart. The PImMS camera then snaps a 3-D picture of the molecular debris.

By firing a laser pulse at later and later times at excited molecules, the researchers can use the PImMS camera to take snapshots of molecules at various stages while they fall into lower energy states. The result is a series of 3-D blow-by-blow images of a molecule changing states.

The researchers tested their approach on a molecule called C2F3I. Although a relatively small molecule, it fragmented into five different products in their experiments. The data and analysis software is available online as part of an open science initiative, and although the results are preliminary, Hockett said, the experiments demonstrate the power of this technique.

"It's effectively an enabling technology to actually do these types of experiments at all," Hockett said. It only takes a few hours to collect the kind of data that would take a few days using conventional methods, allowing for experiments with larger molecules that were previously impossible.

Then researchers can better answer questions like: How does quantum mechanics work in larger, more complex systems? How do excited molecules behave and how do they evolve?

"People have been trying to understand these things since the 1920s," Hockett said. "It's still a very open field of investigation, research, and debate because molecules are really complicated. We have to keep trying to understand them."
-end-
The article, "Time-resolved multi-mass ion imaging: femtosecond UV-VUV pump-probe spectroscopy with the PImMS camera," is authored by Ruaridh Forbes, Varun Suresh Makhija, Kevin Veyrinas, Albert Stolow, Jason Lee, Michael B. Burt, Mark Brouard, Claire Vallance, Iain Wilkinson, Rune Lausten and Paul Hockett. The article will appear in The Journal of Chemical Physics April 4, 2017 (DOI: 10.1063/1.4978923). After that date, it can be accessed at http://aip.scitation.org/doi/full/10.1063/1.4978923.

ABOUT THE JOURNAL

The Journal of Chemical Physics publishes concise and definitive reports of significant research in the methods and applications of chemical physics. See http://jcp.aip.org.

American Institute of Physics

Related Mass Spectrometry Articles:

Proximity of hospitals to mass shootings in US
Nontrauma center hospitals were the nearest hospitals to most of the mass shootings (five or more people injured or killed by a gun) that happened in the US in 2019.
Chemists use mass spectrometry tools to determine age of fingerprints
Chemists at Iowa State University may have solved a puzzle of forensic science: How do you determine the age of a fingerprint?
Keeping guns away from potential mass shooters
Researchers from Michigan State University measured the extent to which mass shootings are committed by domestic violence perpetrators, as well as identyifying how they illegally obtain guns, suggesting how firearm restrictions may prevent these tragedies.
Who is left behind in Mass Drug Administration?
Ensuring equity in the prevention of neglected tropical diseases (NTDs) is critical to reach NTD elimination goals as well as to inform Universal Health Coverage (UHC).
A mechanism capable of preserving muscle mass
By studying the young and aging muscles in mice, researchers from the Myology Research Center (Sorbonne Universite-Inserm) of the Institute of Myology identified a protein, CaVbeta1E that activates the factor GDF5.
Eyeballing a black hole's mass
There are no scales for weighing black holes. Yet astrophysicists from the Moscow Institute of Physics and Technology have devised a new way for indirectly measuring the mass of a black hole, while also confirming its existence.
Changes in gun purchases after mass shootings
For this analysis, researchers examined monthly data on US background checks for gun purchases and permits from November 1998 through April 2016, and they looked for purchasing trends after mass shootings during that time.
Study links perimenopause to accelerated fat mass gains, lean mass losses
A UCLA-led study confirms what women approaching menopause have long suspected: menopause does make fat go up.
Paleontology: Diversification after mass extinction
A team led by Ludwig-Maximilians-Universitaet in Munich paleontologist Adriana López-Arbarello has identified three hitherto unknown fossil fish species in the Swiss Alps, which provide new insights into the diversification of the genus Eosemionotus.
Mass spectrometry sheds new light on thallium poisoning cold case
In 1994, Chinese university student Zhu Ling began experiencing stomach pain, hair loss and partial paralysis.
More Mass Spectrometry News and Mass Spectrometry Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Clint Smith
The killing of George Floyd by a police officer has sparked massive protests nationwide. This hour, writer and scholar Clint Smith reflects on this moment, through conversation, letters, and poetry.
Now Playing: Science for the People

#562 Superbug to Bedside
By now we're all good and scared about antibiotic resistance, one of the many things coming to get us all. But there's good news, sort of. News antibiotics are coming out! How do they get tested? What does that kind of a trial look like and how does it happen? Host Bethany Brookeshire talks with Matt McCarthy, author of "Superbugs: The Race to Stop an Epidemic", about the ins and outs of testing a new antibiotic in the hospital.
Now Playing: Radiolab

Dispatch 6: Strange Times
Covid has disrupted the most basic routines of our days and nights. But in the middle of a conversation about how to fight the virus, we find a place impervious to the stalled plans and frenetic demands of the outside world. It's a very different kind of front line, where urgent work means moving slow, and time is marked out in tiny pre-planned steps. Then, on a walk through the woods, we consider how the tempo of our lives affects our minds and discover how the beats of biology shape our bodies. This episode was produced with help from Molly Webster and Tracie Hunte. Support Radiolab today at Radiolab.org/donate.