Featured Research

from universities, journals, and other organizations

How not to blow up a molecule

Date:
July 30, 2010
Source:
DOE/Lawrence Berkeley National Laboratory
Summary:
Can single-shot imaging with femtosecond x-ray pulses from powerful new free electron lasers really work, or will the beam damage the sample too quickly? Pulse length is the key. A new study reveals that "frustrated absorption" explains why ultrashort pulses, even if their peak power is greater, do less damage to molecules than longer pulses.

High-charge-state ions in a molecule cause strong Coulomb forces, repulsive forces that try to blow its atoms apart. But the research team's crucial finding was that a way to produce only lower charge states in nitrogen molecules is with shorter pulse lengths, even though their peak power is higher.

Related Articles


When pulses are seven femtoseconds or less in duration, their photons are moving through the atom so close together that Auger decay often can't fill up core holes fast enough for photons later in the pulse to photoionize them again. Unfilled holes mean fewer inner electron targets. The number of higher charge states falls off sharply.

The researchers named this phenomenon "frustrated absorption," a molecular mechanism that protects the integrity of molecules by preventing their constituent atoms from being stripped of the outermost valence electrons that hold them together.

"Molecules aren't just atoms stuck together," Gessner remarks. "To understand how molecules are damaged, you have to study the molecules themselves. Although the molecular system we studied is very simple, our result is a start at describing the quantitative damage an illuminating pulse is liable to do to your target."

Free-electron-laser light sources, such as the Linac Coherent Light Source (LCLS) at the SLAC National Accelerator Laboratory, arrived on the scene promising a unique scientific capability: "single-shot imaging." The idea is that a single, short-enough pulse of bright x-rays can generate enough information about a sample, perhaps a virus or a strand of DNA, to record the position of all its atoms before the energetic pulse blows the sample apart.

"This is a new kind of light, which mankind has never seen before," says Oliver Gessner of Berkeley Lab's Ultrafast X-ray Science Laboratory in the Chemical Sciences Division (CSD). "Until now, no one has ever tested what ultrashort pulses of ultra-intense x-rays, delivering an enormous amount of power in a very short time, actually do to molecules. Can molecules really be imaged in a single shot, or will radiation damage them or destroy them too quickly?"

Gessner led the Berkeley Lab contingent of a multinational collaboration that used the LCLS's Atomic, Molecular and Optical Science instrument to study what effects femtosecond x-ray pulses (a femtosecond is 10-15 seconds, a quadrillionth of a second) had on a simple molecular system, nitrogen. Gessner and his CSD colleagues Oleg Kornilov and Stephen Leone, working with Stephen Pratt of Argonne National Laboratory and other key members of the team, performed the critical analysis and interpretation of the data and modeled the physics of what turned out to be quite a surprising experiment.

The experiment called for blasting nitrogen molecules with pulses ranging from 280 to only four femtoseconds in duration. Since each pulse packed the same number of photons (particles of light), the peak power increased as the pulses grew shorter. Nevertheless, the shortest pulses did the least damage.

Nora Berrah and Matthias Hoener of Western Michigan University, guests at Berkeley Lab's Advanced Light Source, were respectively the principal investigator and the first author of the paper reporting the results, which appeared in the 25 June 2010 issue of Physical Review Letters.

Taking nitrogen apart

Each of a nitrogen molecule's two atoms has seven electrons. At the LCLS the research team worked with 1.1-nanometer wavelength x-rays (a nanometer is a billionth of a meter), whose photons interact almost exclusively with an atom's core electrons, those in orbitals nearest the nucleus. When a photon knocks an inner electron out of an atom, one of the outer electrons quickly falls into the hole, in a process called Auger decay that provides enough energy for a third electron to be ejected from the atom. This leaves the atom "doubly ionized" -- short a total of two electrons, thus having +2 positive charge.

If more photons in the same x-ray pulse hit the same atom, core electrons can be ejected over and over again, each ionization event being followed by Auger decay -- or, in the case of extremely bright pulses, even creating double core holes in a nitrogen molecule, with both in the same atom or one hole in each.

It was no surprise to the researchers that a "long" pulse of high-energy x-rays (280 quadrillonths of a second long!), hitting the atom with one photon after another, could strip an atom of all seven of its electrons, reducing it to a bare core of +7 positive charge.

From these observations, the research team constructed a model that may allow future researchers at the LCLS and similar facilities to calculate what kind of image distortion to expect from pulses of different lengths. The bottom line would appear to be: the shorter the pulse the less the damage.


Story Source:

The above story is based on materials provided by DOE/Lawrence Berkeley National Laboratory. Note: Materials may be edited for content and length.


Journal Reference:

  1. Hoener et al. Ultraintense X-Ray Induced Ionization, Dissociation, and Frustrated Absorption in Molecular Nitrogen. Physical Review Letters, 2010; 104 (25): 253002 DOI: 10.1103/PhysRevLett.104.253002

Cite This Page:

DOE/Lawrence Berkeley National Laboratory. "How not to blow up a molecule." ScienceDaily. ScienceDaily, 30 July 2010. <www.sciencedaily.com/releases/2010/06/100625101112.htm>.
DOE/Lawrence Berkeley National Laboratory. (2010, July 30). How not to blow up a molecule. ScienceDaily. Retrieved December 21, 2014 from www.sciencedaily.com/releases/2010/06/100625101112.htm
DOE/Lawrence Berkeley National Laboratory. "How not to blow up a molecule." ScienceDaily. www.sciencedaily.com/releases/2010/06/100625101112.htm (accessed December 21, 2014).

Share This


More From ScienceDaily



More Matter & Energy News

Sunday, December 21, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Touch-Free Smart Phone Empowers Mobility-Impaired

Touch-Free Smart Phone Empowers Mobility-Impaired

Reuters - Innovations Video Online (Dec. 21, 2014) A touch-free phone developed in Israel enables the mobility-impaired to operate smart phones with just a movement of the head. Suzannah Butcher reports. Video provided by Reuters
Powered by NewsLook.com
Building Google Into Cars

Building Google Into Cars

Reuters - Business Video Online (Dec. 19, 2014) Google's next Android version could become the standard that'll power your vehicle's entertainment and navigation features, Reuters has learned. Fred Katayama reports. Video provided by Reuters
Powered by NewsLook.com
AP Review: Nikon D750 and GoPro Hero 4

AP Review: Nikon D750 and GoPro Hero 4

AP (Dec. 19, 2014) What to buy an experienced photographer or video shooter? There is some strong gear on the market from Nikon and GoPro. The AP's Ron Harris takes a closer look. (Dec. 19) Video provided by AP
Powered by NewsLook.com
Obama: Better Ways to Create Jobs Than Keystone Pipeline

Obama: Better Ways to Create Jobs Than Keystone Pipeline

AFP (Dec. 19, 2014) US President Barack Obama says that construction of the Keystone pipeline would have 'very little impact' on US gas prices and believes there are 'more direct ways' to create construction jobs. Duration: 00:47 Video provided by AFP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins