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= Carl Lineberger =

Early Life and Education
Carl Lineberger was born on December 5, 1939 in Hamlet, North Carolina. His parents were Caleb Henry, who worked for the Seaboard Railroad, and Evelyn Pelot Cooper, a homemaker. From a young age, Lineberger demonstrated an acute interest in electricity. His father would bring home electrical odds and ends from the railroad and encourage him to play with them, thus stimulating Linenberger’s enthusiasm for electronics. This prompted Lineberger to scavenge up the materials to successfully build a crystal radio and he became an amateur radio operator by the age of ten.

While acting as a ham operator (W4YLL) for the following six years he also learned to build instruments and passed the electronics exam and Morse code speed test required for an amateur radio operator license, even without mathematical training. His interest in radios transitioned to a passion for building high power transmitters, receivers and antennas. At age 12, Lineberger decided to pursue electrical engineering.

As Lineberger entered high school, his interest in chemistry grew as he was provided the opportunity to experiment freely in the chemistry laboratories alone instead of attending conventional class. This was a result of a mutual dislike between him and his chemistry teacher, but lead to his experimenting with large-scale thermite reactions in order to put on a demonstration for a parent-teacher meeting. His final two years were also filled with an independent science fair project: he attempted to build a He+ field ion emission microscope. While he easily obtained the appropriate electronics, tip preparation and Phosphor screen preparation, he couldn’t acquire the appropriate materials for the vacuum components and instead opted to build a near-infrared transmitter / receiver.

As he was starting at Georgia Tech, Lineberger was having doubts about electrical engineering, due to his already expansive knowledge in Circuits, Electricity and Magnetism, and Antennas. However, since the chemistry and physics majors did not have enough math courses in their curriculums, so he opted to stay in electrical engineering. Due to the fact that Lineberger stayed in EE, he was required to take an introductory chemistry course, which happened to be taught by an assistant professor Peter Sherry, an influential figure in Lineberger’s career. After the first exam, Sherry recommended that Lineberger and a few other top students stop attending general chemistry and instead meet with him in the evenings to learn physical chemistry.

For the next three years, Lineberger participated in ample extracurricular activities, but at the end of the third year quit all of them to work at the Georgia Tech Engineering Experimental Station. He then began working on a project analyzing electrical, thermal, cohesive, and corrosion-resistance properties of thin metal films in electronics using tungsten and gold, funded by the Western Electric Company. This opportunity allowed him to work with the vacuum system he was interested in during his high school science project and confirmed his enthusiasm about working in a laboratory. After completing his final year while working at the engineering experimental station, he decided to stay at Georgia Tech for graduate school.

Academic Career
During Lineberger’s third year in his undergraduate career, Lineberger took a class called “The Physical Basis for Electrical Engineering” that allowed him to rediscover his scientific passion for understanding nature on the atomic level. After taking the class that was at the time taught by professor John Hooper, Lineberger decided to cease all extracurricular activities in order to pursue a full time job at the Georgia Tech Engineering Experimental Station (analogous to to MIT’s Lincoln Laboratories). It was here when Lineberger began to perform his own work on the electrical, thermal, cohesive, and corrosion-resistance properties of gold and tungsten thin films to be used in the electronics industry.

With funding provided by the Western Electric Company, Lineberger was able to build and operate the vacuum system that he designed for his high school science fair project. From his time at Georgia Tech, Lineberger also became fond of working in a laboratory setting. Lineberger’s job with the Georgia Tech Engineering Experimental Station kept him occupied until senior year when he decided to attend graduate school at Georgia Tech to pursue a Master’s degree in Electrical Engineering.

Lineberger completed his Ph.D. at Georgia Tech under the guidance of John Hooper and Earl McDaniel, an electrical engineering and physics professor. During his graduate school years from 1961 to 1964, Lineberger worked in an electrical engineering laboratory where he collaborated with Hooper and McDaniel to design an electron-ion crossed-beam apparatus. In 1965, Lineberger became an associate professor in the Electrical Engineering department at Georgia Tech where he taught modern physics and atomic collisions. About halfway into his graduate career, Lineberger discovered an institute created as a partnership between the National Bureau of Standards and the University of Colorado, Boulder. The institution’s name was JILA and it was a collaboration of the Astrophysics, Aerospace Engineering, Chemistry, and Physics Departments at the University of Colorado.

Since Lineberger worked as a research physicist in the U.S. Army Ballistic Research Laboratory from 1965-1968, it was not until August 1968 when he began working at JILA. Lineberger worked on an experiment involving a flashlamp-pumped tunable dye laser developed by Peter Sorokin. Within a couple of weeks, Lineberger and his colleagues Jan Hall, Don Jennings, and Art Schmeltekopf, were capable of designing the first high-resolution tunable-laser photodetachment apparatus capable of producing adequate results. From 1970-1972, Lineberger acted as an Assistant Professor of Chemistry at the University of Colorado and in 1972, he was promoted to the title of Associate Professor. As a new faculty member, Lineberger became so absorbed in his work that his marriage with Aileen ended in 1971.

Not shortly after, Lineberger was extended a tenure track position in the Department of Chemistry at the University of Colorado, Boulder. This occasion was rather unconventional since Lineberger came from an electrical engineering background; however, Lineberger was hired by the Department of Chemistry due to the praise of notable faculty members. In 1982, Carl Lineberger acted as a visiting professor to both Stanford University and the University of Chicago. From 1985-1986, Lineberger served as the chair for JILA. As of 1985 to present day, Lineberger is an E.U. Condon Distinguished Professor of Chemistry at the University of Colorado.

Scientific Contributions and Research
Dr. Lineberger has made numerous contributions to the National Institute of Standards and Technology, especially in the measurement of the properties of certain anions using laser photoelectron spectrometry in the 1970’s. The results that Lineberger’s lab derived are still used today when searching NIST’s database for Lineberger’s contributions. Some compounds that Lineberger has studied include but are not limited to nitrogen anion, PO anion, CCl2-, methanediylium anion, and cyclopentadienide anion. Much of this data was published by Dr. Lineberger in the Journal of Physical and Chemical Reference Data. More recently his research has focused on photoelectron spectroscopy of metal cluster anions, published in Journal of Chemical Physics.

Dr. Lineberger’s current research at the University of Colorado, Boulder focuses on three main areas: Caging Dynamics, Photoelectron Imaging, and Photoelectron Spectroscopy. All three areas, however, fit into a niche of physical chemistry. His lab investigates the structure and stability of ions, photoelectron spectroscopy of anions, and photophysics and dynamics of cluster ions using instruments that detect the interaction of laser radiation with mass-selected ion beams. A result of this method is both a high degree of precision and accuracy, but also the ability to measure molecular reaction dynamics in real time. When not using laser radiation to measure reaction dynamics, Dr. Lineberger’s lab group focuses on using photoelectron spectroscopy of negative ions to measure negative ion structure.

The purpose of caging dynamics, or ultrafast photodetachment photoionization spectroscopy is to explore the dynamics of neutral species through electron photodetachment from precursor anions. This research follows the central theme of discovering data about compounds through the study and manipulation of their anions. This technique is also called Charge Reversal Spectroscopy (CRS). Here, a high energy electron beam is shot at a pulsed gas jet to produce a source of anions of the desired compound. The negative ion packed is then extracted and shot and filtered through a mass gate. The selected anions then reverted first to neutral species, then to cations by a femtosecond pump laser and probe laser, respectively. The positive and neutral species are then detected and measured after separation. The cation signal is recorded at various time delays between pump and probe photons. This is done to gain information about neutral wavepacket propagation, and thus sheds light on the neutral species.

The other main area of focus in Dr. Lineberger’s research is photoelectron imaging. Photoelectron imaging is an experimental technique that combines photoelectron spectroscopy and a photographic approach to yield images of the photoelectron probability distributions. The photoelectron distributions analyzed are of photoelectrons that become detached from gas-phase chemical systems. The experimental technique involves using pulsed laser and ion beams to shoot ions of interest at an imaging detector. From a static electric field generated by velocity-map imaging electrodes, photoelectrons are projected onto a detector and the corresponding photoelectron distributions are focused onto a longitudinal plane of the detector. The probability distributions are then developed by the accumulation of approximately 105 single electron impacts. One motivation for developing the technique of photoelectron imaging is to use it as a quantum chemistry visualization tool.

Lineberger explored the properties of Dicyanamide N(CN),  a common anion of ionic liquids. Since dicyanamide is an anion, it displays hypergolic behavior when combined with cations. This means that is ignites spontaneously when mixed with certain cations. Not only does this generate ionic liquids, but dicyanamide in particular generates ionic liquids with low viscosities. In practical applications, such as propulsion, this is important for efficient delivery, making dicyanamide an important compound for fuels. Dicyanamide is also one of the few anions that has not been shown to react with Hydrogen, the most astronomically abundant element.

Lineberger and his lab determined dicyanamide to be a very stable species, with an experimental electron-binding energy of 4.135 ± 0.010 eV. In order to characterize dicyanamide’s reactivity, they explored its reactivity with whole gamut of molecular species. Nitric acid was the only neutral reagent that reacted rapidly enough to be detected by selected ion flow tube (SIFT) measurements. The reaction of dicyanamide with nitric acid proceeded with a bimolecular reaction rate constant of 2.7x 10-10 cm3/s at a pressure of 0.45 Torr. Based on this lack of reactivity of dicyanamide, Lineberger and his laboratory hypothesize that dicyanamide exists in molecular clouds of interstellar medium. This has been corroborated by spacecraft Cassini’s voyage to Saturn’s moon Titan. Cassini collected mass spectra of Titan’s nitrogen- and methane- rich atmosphere, and the mass spectrum showed a strong peak corresponding to 66 m/z. This strongly suggest the presence of dicyanamide in Titan’s atmosphere. Measurements of the microwave spectrum for this anion would allow astronomers to search for this molecule in astrochemical environments. Moreover, the mixing of nitric acid with ionic liquids containing dicyanamide resulted in hypergolic behaviour. This suggests that dicyanamide can be used possibly as a next-generation bipropellant hypergolic fuels, facilitating the current effort to replace hydrazine fuels, which are dangerous because of their toxic, volatile, and corrosive nature.

Previous studies conducted by Chambreau and co-workers determined that dicyanamide reacts with two nitric acid molecules to form deprotonated 1,5-dinitrobiuret. Lineberger and his lab characterized this mechanism. A key step in the formation of 1,5-dinitrobiuret is the proton transfer from nitric acid to dicyanamide. Computational modeling showed that dicyanamide has two protonation sites: a terminal nitrile and a central nitrogen. Computational and experimental studies showed that it is more favorable to protonate dicyanamide on the terminal nitrile than on the central nitrogen. Computational studies also indicate that the association of dicyanamide with nitric acid is exothermic by 25 kcal/mol. It is this energy that Lineberger suspects to be responsible for the hypergolic behavior upon mixing nitric acid with ionic liquids containing dicyanamide.

Lineberger has been working on photoelectron spectroscopy since 1975, when he was working to determine the electron affinity of CH, to which he states ," this work has essentially gone completely unnoticed." While this may be, in 1976, his method while researching methylene negative ion has become important to provide bond strengths for thermochemical cycles. This was done by handling diazomethane in 1-cm3 quantities which generated a beam of CH-2 anion. While this experiment showed the expected spectral shifts, hot bands were produced from the bending vibrational excitation of the anion, which would contribute to the spectrum. The anion beam was then altered to try to reduce the hot bands but there was no change in the observed spectrum. It was published that the singlet-triplet splitting of methylene was 19.6 kcal mol-1, even though the highest calculations approximated it to be 8 kcal mol-1.

In the following five years, this experiment would be finessed in order to reach a realistic value. This was finally done by electron impact of ethylene and cooled in helium flow. This new equipment showed that there were hot bands in the previous experiment and the new measurement of the singlet-triplet splitting was 9.00±0.09 kcal mol-1. With this new ability to synthesize anions, this technique was used to obtain electron affinities of organic-reaction intermediates and radicals.

Works
Dr. Lineberger published over 250 publications throughout his career. His earliest textbook contribution was in 1964, when he published “Collision Phenomena in Ionized Gases.” In 1966, Dr. Lineberger’s two-part paper on “Absolute cross sections for single ionization of alkali ions by electron impact” was published in the Physical Review. The paper was based on experiments and measurements that were also the basis of his Ph.D. Thesis. Dr. Lineberger conducted these experiments in collaboration with John Hooper under the guidance of Earl McDaniel, Professor of Electrical Engineering and Physics at the Georgia Institute of Technology.

Dr. Lineberger then went on to publish the “Chemical and Biochemical Applications of Lasers” and “Advances in Mass Spectrometry” in the 1970s. Later in his career, after having made many scientific contributions to the field of quantum chemistry, Dr. Lineberger published chapters in “Femtochemistry and Femtobiology: Ultrafast Reaction Dynamics at Atomic-Scale Resolution” in 1966, and in “The Physics and Chemistry of Clusters” in 2000.

His most recognizable publications were based on his research on Negative Ion Photoelectron Spectroscopy. Dr. Lineberger pioneered the instrument to perform photoelectron spectroscopy (PES). The negative ions, formed at an ion source, are pulled into a high vacuum region and pass through a mass filter to be mass analyzed. The apparatus is able to analyze the energy of electrons after they have been photodetached from the crossing of a negative ion beam and an ion laser.

Dr. Lineberger published three papers on studies he conducted using this technique in 1986 alone. Furthermore, these initial publications went on to become the basis of the periodic table of atomic electron affinities, that is now found in general chemistry textbooks all over the world. Since then, photoelectron spectroscopy has been the foundation of a substantial portion of Dr. Lineberger’s research.

Awards
The following are Lineberger's most notable awards throughout his career: His most recent award was the NAS Award in the chemical sciences. He won this award for his research on molecular negative ion photoelectron spectroscopy. This research has been used to study small molecules, highly reactive short-lived species, and to observe the structure and evolution of molecules undergoing chemical reactions. His research on photoelectron spectroscopy is also used to determine electron affinities of neutral versions of atoms or molecules.
 * Herbert P. Broida Prize in Atomic and Molecular Spectroscopy or Chemical Physics, American Physical Society, 1981
 * Bomem-Michelson Prize, 1987
 * William F. Meggers Prize, Optical Society of America, 1988
 * American Physical Society Earle K. Plyler Prize, 1992
 * American Chemical Society Irving Langmuir Prize in Chemical Physics, 1995
 * American Chemical Society Peter Debye Award in Physical Chemistry, 2004
 * NAS Award in Chemical Sciences, 2015