PHYSICAL CHEMISTRY. Physical chemistry developments of note covered in C&EN this year involved bond-selective chemistry, postcollision rotation, and ultrafast X-rays.

BOND-SELECTIVE Levis, Rabitz, and Menkir found that acetophenone molecules (upper left) interact with intense, tailored laser pulses to produce selective bond rearrangement and cleavage. The upper pulse is shaped to cleave the phenyl-carbonyl bond, producing C6H5 and CH3CO, whereas the lower pulse rearranges the parent compound to produce toluene and CO.

In the area of quantum control of chemical reactions, chemistry professors Robert J. Levis at Wayne State University, Detroit, and Herschel A. Rabitz at Princeton University, working with Wayne State graduate student Getahun Menkir, used computer-guided learning algorithms and strong laser fields to selectively control bond breaking and bond making in organic molecules, such as acetophenone and trifluoroacetone [Science, 292, 709 (2001); C&EN, May 28, page 38]. "What's unique about this work is that they have managed not only to selectively break certain bonds, but to create new bonds," a researcher commented. "That is really new." Laser control has potential applications in chemical reactions, quantum computing, materials discovery, analytical chemistry, and other areas.

Also this year, the clockwise or counterclockwise direction in which gaseous diatomic molecules rotate after inelastic collisions was measured for the first time. Associate chemistry professor Joseph Cline of the University of Nevada, Reno, chemist David W. Chandler of Sandia National Laboratories, and coworkers determined the preferred sense of rotation of NO molecules after argon atom bombardment by using circularly polarized light as a molecular probe [Science, 292, 2063 (2001); C&EN, Sept. 17, page 9]. The findings have important implications for studies of gas-phase reaction dynamics.

A new technique to control high-energy X-ray beams on an ultrafast timescale was developed by University of Michigan physicists Matthew F. DeCamp, David A. Reis, and Philip H. Bucksbaum and coworkers [Nature, 413, 825 (2001); C&EN, Oct. 29, page 12]. By shining intense laser light on a thin germanium crystal while the crystal was transmitting X-rays, the researchers were able to switch the X-ray beams on and off on a subpicosecond timescale. The technique could facilitate highly time-resolved studies of atomic position changes and other phenomena in chemical reaction dynamics.

And most recently, physicists at the Photonics Institute of Vienna University of Technology, including Reinhard Kienberger, Michael Hentschel, and Ferenc Krausz, found a way to produce 650-attosecond (650 * 10^–18-second) X-ray bursts--the shortest X-ray pulses ever obtained [Nature, 414, 509 (2001); C&EN, Dec. 3, page 11]. The researchers generated the attosecond pulses by irradiating neon with femtosecond bursts of red light and then filtering the high-frequency X-ray pulses emitted in response. The technique could make it possible to study chemical dynamics phenomena occurring on faster timescales than those accessible by femtosecond (10^–15-second) spectroscopy, the Nobel Prize-winning approach that has represented the state-of-the-art ultrafast spectroscopy technique until now.