38 research outputs found
OVERTONE AND COMBINATION BAND SPECTROSCOPY OF JET COOLED METHANOL
No full text[1] H.L. Fang, D.M. Meister, R.L. Swofford, J. Phys. Chem. 88, 405-409 (1984). [2] O.V. Boyarkin, L. Lubich, R.D.F. Settle, D.S. Perry, T.R. Rizzo, J. Chem. Phys. 107, 8409-8422 (1997).Author Institution: Lab. de Chimie Physique Mol\'eculaire, INSTITUT DE CHIMIE PHYSIQUE MOLECULAIRE; Lab. de Chimie Physique Mol\'eculaire, UNIVERSITY OF AKRON; DEPARTMENT OF CHEMISTRY, UNIVERSITY OF AKRONOvertone spectra of jet-cooled methanol have been recorded from 5,000 to using Infrared Laser Assisted Photofragment Spectroscopy (IRLAPS) for the detection of the vibrationally excited molecules. In addition to the OH stretch overtones , the major components of the spectra are the overtones of the CH stretch (up to ) as well as combinations of the OH stretch with the CO stretch , the COH bend , and both . These data, together with photoacoustic data [1] up to and previously reported IRLAPS data [2] up to have been fit to an anharmonic Hamiltonian. In this Hamiltonian, the CH stretch vibrations are treated as a pair of local modes, and for and higher. The other modes are treated as the usual normal vibrations
Method of calculation of a thermolysis and friction of a turbulent disperse flow in nozzles
No full textTORSIONAL ANALYSIS OF METHANOL IN THE OH VIBRATIONAL MANIFOLD UP TO
No full textAuthor Institution: Department of Chemistry, University of Akron; Laboratoire de chimie physique mol\'{e}culaire, Ecole Polytechnique F\'{e}d\'{e}rale de LausanneTorsional analyses of OH overtone bands of methanol, including , and 6, are reported. The rotationally resolved spectra at each level were obtained in Lausanne by double resonance excitation and IRLAPS (infrared laser-assisted photodissociation spectroscopy) detection. The data reveal approximately regular torsional energy patterns with a monotonically decreasing torsional tunnelling splitting from on the ground state to at . The torsional tunnelling splittings, together with two different models for the vibrational dependence of the torsional moment of inertia, are used to estimate the torsional barrier heights. The data are consistent with an approximately linear increase in the torsional barrier height from in the ground state of 612 or at
Quantification of enantiomers and blind identification of erythro-sphingosine non-racemates by cold ion spectroscopy
No full textEnantiomers of a lipid erythro-sphingosine have been quantified with ≈4% accuracy by UV cold ion spectroscopy of their non-covalent complexes with a chiral aromatic molecule. The diastereomeric configuration of such complexes enables the quantification using just a single enantiomeric lipid standard and the identification of non-racemic solutions with no standards at all.SCI-SB-R
Intramolecular energy transfer in highly vibrationally excited methanol. III. Rotational and torsional analysis
No full textWe report here torsional analysis of rotationally resolved spectra of the 3 nu(1), 5 nu(1), and 6 nu(1) (OH stretch) bands of jet-cooled methanol. The upper states are reached by a double resonance excitation scheme involving the selection of single rotational states in the n1 fundamental band. Detection of the overtone transitions (n nu(1)<--nu(1)) is by infrared laser assisted photofragment spectroscopy (IRLAPS). The torsional tunneling frequency declines monotonically from 9.1 cm(-1) in the vibrational ground state to 1.6 cm(-1) at 6 nu(1). For the available rotational levels at 3 nu(1) (K = 0-3) and 6 nu(1) (K = 0,1), the pattern of torsional energies is approximately regular. To obtain the vibrational dependence of the torsional barrier V-3, it was necessary to use the OH radical and HOOH as models for the vibrational dependence of the torsional inertial constant F. The assumed linear dependence of V-3 on nu(1) accounts for the torsional tunneling splittings at nu(1) = 0, 3, and 6 and for the pattern of the torsional energies. V-3 increases by 40-45 cm(-1) per quantum of OH excitation. (C) 1999 American Institute of Physics. [S0021-9606(99)02417-4].LCP
Microhydration of Biomolecules: Revealing the Native Structures by Cold Ion IR Spectroscopy
No full textThe native-like structures of protonated glycine and peptide Gly3H+ were elucidated using cold ion IR spectroscopy of these biomolecules hydrated by a controlled number of water molecules. The complexes were generated directly from an aqueous solution using gentle electrospray ionization. Already with a single retained water molecule, GlyH+ exhibits the native-like structure characterized by a lack of intramolecular hydrogen bonds. We use our spectra to calibrate the available data for the same complexes, which are produced by cryogenic condensation of water onto the gas-phase glycine. In some conformers of these complexes, GlyH+ adopts the native-like structure, while in the others, it remains “kinetically” trapped in the intrinsic state. Upon condensation of 4–5 water molecules, the embedded amino acid fully adopts its native-like structure. Similarly, condensation of one water molecule onto the tripeptide is insufficient to fully eliminate its kinetically trapped intrinsic states.LCP
Vibrational Overtone Spectra of Jet‐Cooled CF3H by Infrared Laser Assisted Photofragment Spectroscopy
No full textUsing our recently developed technique of infrared laser assisted photofragment spectroscopy (IRLAPS), we have measured four vibrational overtone bands of jet-cooled CF3H in the N = 4 and N = 5 CH stretch-bend polyads. The cooling in the expansion eliminates much of the rotational congestion and reveals homogeneous structure which reflects the vibrational coupling of the stretch bend states with other modes of the molecule. This homogeneous structure indicates that the coupling of the stretch-bend slates to the rest of the molecule is 20-2000 times weaker than the stretch bend coupling itself and implies a hierarchy of time scales in the vibrational energy redistribution of the excited molecule. The overtone spectra of the jet-cooled molecules also reveal a wide variation in the coupling strengths of the stretch-bend states to the other modes, suggesting that the coupling depends upon the presence of specific low-order resonances rather than on the total density of states.LCP
Microhydration Effects on the Encapsulation of Potassium Ion by Dibenzo-18-Crown-6
Get PDFWe have measured electronic and conformer-specific vibrational spectra of hydrated dibenzo-18-crown-6 (DB18C6) complexes with potassium ion, K+center dot DB18C6 center dot(H2O)(n) (n = 1-5), in a cold, 22-pole ion trap. We also present for comparison spectra of Rb+center dot DB18C6 center dot(H2O)(3) and Cs+center dot DB18C6 center dot(H2O)(3) complexes. We determine the number and the structure of conformers by analyzing the spectra with the aid of quantum chemical calculations. The K+center dot DB18C6 center dot(H2O)(1) complex has only one conformer under the conditions of our experiment. For K+center dot DB18C6 center dot(H2O)(n) with n = 2 and 3, there are at least two conformers even under the cold conditions, whereas Rb+center dot DB18C6 center dot(H2O)(3) and Cs+center dot DB18C6 center dot(H2O)(3) each exhibit only one isomer. The difference can be explained by the optimum matching in size between the K+ ion and the crown cavity; because the K+ ion can be deeply encapsulated by DB18C6 and the interaction between the K+ ion and the H2O molecules becomes weak, different kinds of hydration geometries can occur for the K+center dot DB18C6 complex, giving multiple conformations in the experiment. For K+center dot DB18C6 center dot(H2O)(n) (n = 4 and 5) complexes, only a single isomer is found. This is attributed to a cooperative effect of the H2O molecules on the hydration of K+center dot DB18C6; the H2O molecules form a ring, which is bound on top of the K+center dot DB18C6 complex. According to the stable structure determined in this study, the K+ ion in the K+center dot DB18C6 center dot(H2O)(n) complexes tends to be pulled largely out from the crown cavity by the H2O molecules with increasing n. Multiple conformations observed for the K+ complexes will have an advantage for the effective capture of the K+ ion over the other alkali metal ions by DB18C6 because of entropic effects on the formation of hydrated complexes.LCP
ULTRAVIOLET AND INFRARED SPECTROSCOPY OF HELICAL PEPTIDES AND THEIR WATER COMPLEXES
No full textAuthor Institution: Laboratoire de Chimie Physique Moleculaire, Ecole Polytechnique Federale de Lausanne, CH-1015, Lausanne, SwitzerlandWe have developed methods to study large, gas-phase molecules at low temperatures by combining electrospray ionization with collisional cooling in a 6 K, 22-pole ion trap, and using ultraviolet photofragmentation and infrared-ultraviolet double resonance spectroscopy to probe molecular structure. An important goal of our studies has been to understand the conformational preferences of increasingly large peptides, and to identify spectroscopic signatures of important secondary structure elements such as helices. In addition to transferring large molecules into the gas phase, electrospray affords the opportunity to create complexes between the ion of interest and a selected number of solvent molecules. We have systematically studied the effects of microsolvation on the small helical peptide Ac-Phe-(Ala)-Lys-H, determining how the structure of the helix changes as up to ten water molecules begin to compete with intramolecular hydrogen bonds
TORSION-ROTATION ANALYSIS OF TORSIONAL COMBINATION BANDS BUILT ON THE METHANOL OH STRETCH OVERTONE: , AND
No full textAuthor Institution: INSTITUT DE CHIMIE PHYSIQUE MOLECULAIRE, EPFL, CH - 1015, LAUSANNE; Department of Chemistry, UNIVERSITY OF AKRON, AKRON, OHIO 44325The spectrum of the first overtone OH stretch band in jet-cooled methanol has been measured using Infrared Laser Assisted Photofragment Spectroscopy (IRLAPS) and detailed assignments have been made. In addition to the torsional fundamental band it was possible to observe and assign the torsional combination band with ( and 2). These transitions are very week but can be clearly resolved in the spectra. In total, 131 transitions reaching 19 different K levels in the state have been fit to a global torsion-rotation Hamiltonian and the leading torsion-rotation parameters have been determined. Assignments for the much weaker and irregular torsional band structure for and are in progress
