Giacinto ScolesFRS (born 1935 in Torino, Italy) is a European and North American chemist and physicist who is best known for his pioneering development of molecular beam methods for the study of weak van der Waals forces between atoms, molecules, and surfaces. He developed the cryogenic bolometer as a universal detector of atomic and molecule beams that not only can detect a small flux of molecules, but also responds to the internal energy of the molecules. This is the basis for the optothermal spectroscopy technique which Scoles and others have used to obtain very high signal-to noise and high resolution ro-vibrational spectra.
Scoles was born in Italy and raised there through the Second World War. A few years after the war he moved, with his family, to Spain, where Scoles spent his adolescence. He returned to Italy and graduated the University of Genoa in 1959 with a degree in Chemistry. His publication record started with “Vapour Pressure of Isotopic Liquids I” published 1959 in Il Nuovo Cimento. Starting his interdisciplinary research between chemistry and physics, in 1960 he was appointed Assistant Professorship in the Physics Department of the University of Genoa where he taught a lab course and conducted experiments on isotope separation during physical adsorption (physisorption).
In 1961, he changed research area and joined Jan Beenakker’s group at the Kamerlingh-Onnes Laboratorium of Leiden University in the Netherlands. There he co-authored one of the first papers on what became soon known as the Senftleben-Beenakker effect:[citation needed] the influence of an external magnetic or electric field on the transport properties of dilute polyatomic gases.[1] The idea behind this effect is that every polyatomic molecule – even a simple paramagnetic one like N2 – has a magnetic moment, due to its end-over-end rotation, which can be used as a handle to make it precess in an external magnetic field. If the precession frequency is sufficiently large compared to the collision frequency, the average kinetic cross section will change, and so will the transport properties. Likewise, for polar molecules one may employ electric fields to achieve the desired precession. This field has yielded a wealth of information on the non-spherical part (i.e. the angle dependence) of the intermolecular potential. In addition, several new phenomena were later discovered that had been believed to be non-existing in neutral gases, like transverse transport effects in a magnetic field, comparable to the Hall effect in electrical conduction.
In 1964, Scoles returned to the University of Genoa as Assistant Professor of Physics. In Genoa he stayed until 1971 and in those years established a renowned molecular beams laboratory devoted to the investigation of intermolecular forces in gases. Most significant was the development of the cryogenic bolometer to detect molecular beams. Bolometers detect tiny heat input (with noise on the order of 10−14watts per square roothertz) and had previously been developed as detectors of Infrared Radiation but here they are used to measure the internal and translational energy of a beam of atoms or molecules. The test apparatus set up together with M. Cavallini and G. Gallinaro[2] offered great advantages with respect to conventional techniques used at that time and reduced the cost of building beam machines.[citation needed] Scoles and his colleagues published a series of key papers which include the determination of the energy dependence of the integral collision cross section of He scattered by He, the observation of “Rainbow Scattering“ between two crossed beams of Argon,[3] the first measurement of orbiting resonances in the scattering between two atoms (Hg and H).[4]
In 1971, Scoles moved to the University of Waterloo, Canada as Professor of Chemistry and Physics. There, he set up the first successful crossed molecular beam laboratory in Canada. He help establish the Waterloo Centre for Molecular Beams and Laser Chemistry, the Centre for Surface Science in Technology, as well as the weekly chemical physics seminars and annual Symposium on Chemical Physics, both of which continue to this day. He was the initial (Acting) Director of the Guelph-Waterloo Centre for Graduate Work in Chemistry, the first true inter-university graduate program in Canada. Scoles performed crossed beam differential scattering cross-section studies of atom-atom, atom-molecule and molecule-molecule interactions,[5] using his bolometer detector. He also began using helium atom diffraction to study the structure of surfaces, both of pure crystals which often undergo change from the bulk structure (reconstruction) and also the structure of overlayers of atoms and molecules absorbed on surfaces. With Terry Gough and then graduate student Roger Miller, Scoles introduced the technique of bolometer-detected optothermal spectroscopy of molecular beams where vibrational excitation of a beam of molecules is detected by the bolometer. They used this technique to studies vibrational dissociation of a complex of two or more molecules held together by Van der Waals forces. By the early 1980s, Scoles began the first studies of the spectroscopy of molecules adsorbed in or on clusters of rare gas atoms.
In the mid-to-late 1970s Scoles spent part of his time at the University of Trento, Italy where he established a new molecular beam laboratory. The activity of the Trento lab was mainly focused on opto-thermal spectroscopy and atomic hydrogen scattering experiments.
Scoles moved to Princeton University in 1986. One of the experiments that Scoles brought to Princeton was the study of IR spectroscopy of molecules attached to inert gas clusters, particularly Ar and Xe clusters. In this work, he developed the now widely used “pickup technique”[6] and set the stage for his later pioneering work on superfluid helium nanodroplets, for which he recently shared the Benjamin Franklin Award in Physics. The helium experiments, started with students S. Goyal and D. Schutt, provided the first molecular spectra of solutes in liquid helium, a unique superfluid solvent.[7] Frank Stienkemeier joined the group as a postdoc and together with graduate students John Higgins and Carlo Callegari (and sabbatical visitor Wolfgang Ernst) established the “Alkali age” of the group which provided a rich vein to explore chemical dynamics in this fascinating state of matter.[8] Graduate student James Reho brought time resolved spectroscopy techniques into the mix.[9]Erik Kerstel did a thesis on subdoppler spectroscopy of hydrogen bonded complexes, including the first such spectra in the vibrational overtone region.[10]Brooks Pate brought Scoles and Kevin K. Lehmann together for what proved to be a long series of experiments (and many Ph.D. theses) that characterized Intramolecular Vibrational energy Redistribution. They first studied the hydrogen stretching fundamental and first overtone spectral regions and observed Lorentzian lineshapes due to irreversible relaxation for large molecules with a very high density of states.[11] They developed IR-microwave and later IR-IR double resonance methods to provide unambiguous quantum assignments of even highly congested spectra and to reach higher in energy.[12] The work by Andrea Callegari on benzene, long a model system for such studies is noted among many such studies. After this work, Carlo Callegari converted the apparatus into a helium droplet machine, which was used for the first study of overtone vibrational transitions in helium nanodroplets. Also, the pure rotational spectra of HCCCN and HCN in helium were observed.[13] This established that a single droplet could absorb several thousand photons without "optically pumping" out of resonance.[citation needed]
Scoles was instrumental in the establishment of the Princeton Materials Institute and became a close collaborator of Peter Eisenberger, its first director. Scoles also brought to Princeton his Helium Diffraction Spectrometer for the study of surface structure.[14] His focus turned from inorganic overlayers to the study of self-assembled monolayers, particularly alkane thiols on Au(111).[15] Scoles collaborated with Eisenberger in using X-Rays as a complementary surface structure tool and showed the power of the combination of the two methods. Scoles developed expertise in atomic force microscopy (AFM) to study surface structure and more recently, tip induced surface modification using the nanografting technique [16,17] which had been previously developed by his former student Gang Yu Liu. In collaboration with Steve Bernasek, Scoles has also studied the influence of vibrational excitation (again for the first time in the first C-H overtone region) on the sticking probability of a molecule (methane) on a metal surface.[16]
Starting in 2003, Scoles returned part-time to Italy, taking appointments at the Trieste Synchrotron Elettra and the International School for Advanced Studies (SISSA), In SISSA he joined the Condensed Matter group where he began collaborating on theoretical problems dealing with helium nanodroplets and with physisorption. At the same time, he started an experimental group in Elettra, focusing on nanoscience, with particular attention to self-assembled monolayers and their properties [19,20]. Later, Scoles expanded his research into nanoscale biological processes, biophysics, and nanomedicine, in connection with the local Consortium of Molecular Biomedicine.
Diatomic molecules are molecules composed of only two atoms, of the same or different chemical elements. If a diatomic molecule consists of two atoms of the same element, such as hydrogen or oxygen, then it is said to be homonuclear. Otherwise, if a diatomic molecule consists of two different atoms, such as carbon monoxide or nitric oxide, the molecule is said to be heteronuclear. The bond in a homonuclear diatomic molecule is non-polar.
Infrared spectroscopy is the measurement of the interaction of infrared radiation with matter by absorption, emission, or reflection. It is used to study and identify chemical substances or functional groups in solid, liquid, or gaseous forms. It can be used to characterize new materials or identify and verify known and unknown samples. The method or technique of infrared spectroscopy is conducted with an instrument called an infrared spectrometer which produces an infrared spectrum. An IR spectrum can be visualized in a graph of infrared light absorbance on the vertical axis vs. frequency, wavenumber or wavelength on the horizontal axis. Typical units of wavenumber used in IR spectra are reciprocal centimeters, with the symbol cm−1. Units of IR wavelength are commonly given in micrometers, symbol μm, which are related to the wavenumber in a reciprocal way. A common laboratory instrument that uses this technique is a Fourier transform infrared (FTIR) spectrometer. Two-dimensional IR is also possible as discussed below.
Raman spectroscopy is a spectroscopic technique typically used to determine vibrational modes of molecules, although rotational and other low-frequency modes of systems may also be observed. Raman spectroscopy is commonly used in chemistry to provide a structural fingerprint by which molecules can be identified.
In physics, Raman scattering or the Raman effect is the inelastic scattering of photons by matter, meaning that there is both an exchange of energy and a change in the light's direction. Typically this effect involves vibrational energy being gained by a molecule as incident photons from a visible laser are shifted to lower energy. This is called normal Stokes-Raman scattering.
Photoemission spectroscopy (PES), also known as photoelectron spectroscopy, refers to energy measurement of electrons emitted from solids, gases or liquids by the photoelectric effect, in order to determine the binding energies of electrons in the substance. The term refers to various techniques, depending on whether the ionization energy is provided by X-ray, XUV or UV photons. Regardless of the incident photon beam, however, all photoelectron spectroscopy revolves around the general theme of surface analysis by measuring the ejected electrons.
Molecular physics is the study of the physical properties of molecules and molecular dynamics. The field overlaps significantly with physical chemistry, chemical physics, and quantum chemistry. It is often considered as a sub-field of atomic, molecular, and optical physics. Research groups studying molecular physics are typically designated as one of these other fields. Molecular physics addresses phenomena due to both molecular structure and individual atomic processes within molecules. Like atomic physics, it relies on a combination of classical and quantum mechanics to describe interactions between electromagnetic radiation and matter. Experiments in the field often rely heavily on techniques borrowed from atomic physics, such as spectroscopy and scattering.
Rydberg ionization spectroscopy is a spectroscopy technique in which multiple photons are absorbed by an atom causing the removal of an electron to form an ion.
Spartan is a molecular modelling and computational chemistry application from Wavefunction. It contains code for molecular mechanics, semi-empirical methods, ab initio models, density functional models, post-Hartree–Fock models, and thermochemical recipes including G3(MP2) and T1. Quantum chemistry calculations in Spartan are powered by Q-Chem.
The helium hydride ion, hydridohelium(1+) ion, or helonium is a cation (positively charged ion) with chemical formula HeH+. It consists of a helium atom bonded to a hydrogen atom, with one electron removed. It can also be viewed as protonated helium. It is the lightest heteronuclear ion, and is believed to be the first compound formed in the Universe after the Big Bang.
A Van der Waals molecule is a weakly bound complex of atoms or molecules held together by intermolecular attractions such as Van der Waals forces or by hydrogen bonds. The name originated in the beginning of the 1970s when stable molecular clusters were regularly observed in molecular beam microwave spectroscopy.
Triatomic hydrogen or H3 is an unstable triatomic molecule containing only hydrogen. Since this molecule contains only three atoms of hydrogen it is the simplest triatomic molecule and it is relatively simple to numerically solve the quantum mechanics description of the particles. Being unstable the molecule breaks up in under a millionth of a second. Its fleeting lifetime makes it rare, but it is quite commonly formed and destroyed in the universe thanks to the commonness of the trihydrogen cation. The infrared spectrum of H3 due to vibration and rotation is very similar to that of the ion, H+ 3. In the early universe this ability to emit infrared light allowed the primordial hydrogen and helium gas to cool down so as to form stars.
Magnesium monohydride is a molecular gas with formula MgH that exists at high temperatures, such as the atmospheres of the Sun and stars. It was originally known as magnesium hydride, although that name is now more commonly used when referring to the similar chemical magnesium dihydride.
The helium dimer is a van der Waals molecule with formula He2 consisting of two helium atoms. This chemical is the largest diatomic molecule—a molecule consisting of two atoms bonded together. The bond that holds this dimer together is so weak that it will break if the molecule rotates, or vibrates too much. It can only exist at very low cryogenic temperatures.
Helium is the smallest and the lightest noble gas and one of the most unreactive elements, so it was commonly considered that helium compounds cannot exist at all, or at least under normal conditions. Helium's first ionization energy of 24.57 eV is the highest of any element. Helium has a complete shell of electrons, and in this form the atom does not readily accept any extra electrons nor join with anything to make covalent compounds. The electron affinity is 0.080 eV, which is very close to zero. The helium atom is small with the radius of the outer electron shell at 0.29 Å. Helium is a very hard atom with a Pearson hardness of 12.3 eV. It has the lowest polarizability of any kind of atom, however, very weak van der Waals forces exist between helium and other atoms. This force may exceed repulsive forces, so at extremely low temperatures helium may form van der Waals molecules. Helium has the lowest boiling point of any known substance.
Neon compounds are chemical compounds containing the element neon (Ne) with other molecules or elements from the periodic table. Compounds of the noble gas neon were believed not to exist, but there are now known to be molecular ions containing neon, as well as temporary excited neon-containing molecules called excimers. Several neutral neon molecules have also been predicted to be stable, but are yet to be discovered in nature. Neon has been shown to crystallize with other substances and form clathrates or Van der Waals solids.
Argon compounds, the chemical compounds that contain the element argon, are rarely encountered due to the inertness of the argon atom. However, compounds of argon have been detected in inert gas matrix isolation, cold gases, and plasmas, and molecular ions containing argon have been made and also detected in space. One solid interstitial compound of argon, Ar1C60 is stable at room temperature. Ar1C60 was discovered by the CSIRO.
Thioxoethenylidene, is a reactive heteroallene molecule with formula CCS.
Dirubidium is a molecular substance containing two atoms of rubidium found in rubidium vapour. Dirubidium has two active valence electrons. It is studied both in theory and with experiment. The rubidium trimer has also been observed.
Diargon or the argon dimer is a molecule containing two argon atoms. Normally, this is only very weakly bound together by van der Waals forces. However, in an excited state, or ionised state, the two atoms can be more tightly bound together, with significant spectral features. At cryogenic temperatures, argon gas can have a few percent of diargon molecules.
Wolfgang Stahl was a German spectroscopist. He was a professor at the RWTH Aachen University.
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