Ethyl alcohol: a case study in asymmetric-asymmetric internal rotation
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molecular spectra↗
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Rotational coherence dominates early-time dynamics and produces long-time revivals in the S 2 state of azulene
Here, the ultrafast dynamics of azulene have been debated for decades, with reported picosecond decay constants variously attributed to intramolecular vibrational redistribution (IVR), internal conversion, or rotational dephasing. Using polarization- and femtosecond time-resolved resonance-enhanced multiphoton ionization spectroscopy with a nanosecond delay window, we disentangle this long-standing inconsistency and show that the early 2–5 ps decay component arises entirely from the rotational dephasing of an excited-state wavepacket. Identical time constants extracted from the decay of the parallel signal and the rise of the perpendicular signal across multiple vibronic origins provide an unambiguous rotational anisotropy signature, eliminating the need for IVR-based interpretations. Extending the measurement window to 1.3 ns reveals well-structured J-type and C-type rotational coherence revivals in S 2 azulene on top of the well-documented fluorescence decay, demonstrating that both the short- and long-time dynamics contain information about the coherent rotational dynamics. These results show that azulene, and by extension polycyclic aromatic hydrocarbons, can sustain structured rotational coherence deep into the nanosecond regime, positioning PAHs as model systems for quantum-coherent wavepacket dynamics and providing a framework for probing coherence, decoherence, and rotational control in electronically rich molecular systems.
Zhan, Jie [University of Georgia, Athens, GA (Unit↗
Rotating shaft seal Patent
Liquid-vapor interface seal design for turbine rotating shafts including helical and molecular pumps and liquid cooling of mercury vapor
Bosco, G. B., Jr.↗
Theoretical models for electron energy relaxation in the lower ionosphere
Elastic collisions and rotation inelastic collisions involving quadrupole molecular transitions are important in energy relaxation of electrons in molecular gases. It has been customary in studying the cooling of electrons in a plasma heated by high-frequency waves to characterize this relaxation by the ionospheric G factor. The G factor is first defined in a fundamental way by use of kinetic theory. Then present models for theoretical cross sections for electron collision with O2 and N2 are used to derive expressions for the G factor in the lower ionosphere. Two models are considered: one uses Gerjuoy-Stein models for both N2 and O2; the other uses a Gerjuoy-Stein model for N2 and a Geltman-Takayanaki model for O2. Neither O2 model has been definitely established experimentally. It is found that temperature dependence of G is critically dependent on the O2 model.
Hagenbuch, K. M.↗
The 1980 summer research fellowship program
The problem of incorporating visual input into robot systems is described. The photochemistry of the stratosphere, particularly possible permutations of the ozone layer, is discussed. Photoelectrochemical properties of metal thio-hypodiphosphates are investigated. Extreme eigenvalues are computed by the Lancqos approach. The rotational Raman spectra of the molecular atmosphere is studied. A computer operated mathematical symbolic manipulation system is described. Preparation of polycrystalline semiconductor electrodes of tungsten and molybdenum dichalcogenides is received.
Darden, G. C.↗
Far-infrared Spectroscopy of Interstellar Gas
Research results of far-infrared spectroscopy with the Kuiper Airborne Observatory are discussed. Both high and intermediate resolution have been successfully employed in the detection of many new molecular and atomic lines including rotational transition of hydrides such as OH, H2O, NH3 and HCl; high J rotational transitions of CO; and the ground state fine structure transitions of atomic carbon, oxygen, singly ionized carbon and doubly ionized oxygen and nitrogen. These transitions have been used to study the physics and chemistry of clouds throughout the galaxy, in the galactic center region and in neighboring galaxies. This discussion is limited to spectroscopic studies of interstellar gas.
Phillips, T. G.↗
Image plane detector spectrophotometer - Application to O2 atmospheric band nightglow
A new variety of low resolution spectrometer is described. This device, an image plane detector spectrophotometer, has high sensitivity and modest resolution sufficient to determine the rotational temperature and brightness of molecular band emissions. It uses an interference filter as a dispersive element and a multichannel image plane detector as the photon collecting device. The data analysis technqiue used to recover the temperature of the emitter and the emission brightness is presented. The atmospheric band of molecular oxygen is used to illustrate the use of the device.
Luo, Mingzhao↗
Ratios of molecular hydrogen line intensities in shocked gas - Evidence for cooling zones
Column densities of molecular hydrogen have been calculated from 19 infrared vibration-rotation and pure rotational line intensities measured at peak 1 of the Orion molecular outflow. The run of column density with energy level is similar to a simple coolng zone model of the line-emitting region, but is not well fitted by predictions of C-shock models current in the literature.
Brand, P. W. J. L.↗
Titan's Atmospheric Composition from Observations by the Cassini Infrared Spectrometer
The Composite Infrared Spectrometer (CIRS) aboard the Cassini spacecraft has been making observations during the fly-bys of Titan since the Saturn-Orbit-Insertion in July 2004. The observations provide infrared them1 emission spectra of Titan s atmosphere in three spectral channels covering the 10/cm to 1400/cm spectral region, with variable spectral resolutions of 0.53/cm and 2.8/cm. The uniquely observed spectra exhibit rotational and vibrational-rotational spectral lines of the molecular constituents of Titan s atmosphere that may be analyzed to retrieve information about the composition, thermal structure, and physical and dynamical processes in the remotely sensed atmosphere. We present an analysis of Titan's infrared spectra observed during July 2004 (TO), December 2004 (Tb) and February 2005 (T3), for retrieval of the stratospheric thermal structure, distribution of the hydrocarbons, nitriles, and oxygen bearing constituents, such as C2H2, C2H4, C2H6, C3H8, HCN, HC3N, CO, and CO2 . Preliminary results on the distribution and opacity of haze in Titan s atmosphere are discussed.
Abbas, M. M.↗
Complex-Valued Intermolecular Coupling Enables Directional Exciton Transport in Excitonic Circuits
Molecular systems capable of directing the flow of excitons are key to the development and optimization of optoelectronic materials. The transport of excitons across multiple molecules is governed by an intermolecular electronic coupling network. In this article, we consider the effects of complex-valued intermolecular electronic coupling on exciton transport. Here, we present a molecular motif capable of generating complex-valued coupling under excitation with circularly polarized light. We use theoretical modeling and simulation to illustrate how complex coupling can be leveraged to drive the rotational flux of excitons in cyclic molecular networks and direct the exciton population in branched molecular networks.
chromophores↗
Far-infrared line intensities of H2O and CO from warm molecular clouds
Takahashi et al. (1983) have studied the role of H2O in the overall energetics of warm molecular clouds with large optical depths. It was found that in molecular clouds associated with nearby or embedded luminosity sources, the dust is likely to be warmer than the molecular gas. Thus, the warm dust represents the primary source of heat for the gas. In some cases, H2O was found to cool the gas. Takahashi et al. (1983) have presented the formalism for treating H2O in an optically thick molecular cloud with embedded sources of luminosity. The total H2O heating and cooling rates were also calculated. In the present investigation, the emergent intensities of far-infrared lines of H2O and excited, rotational CO transitions from relatively warm molecular clouds based on the large-velocity gradient model of the previous study are calculated. It is found that the dominant submillimeter CO transitions are related to emission, while the H2O transitions can be either absorption or emission lines.
Takahashi, T.↗
Supernova remnants in dense clouds. I - Blast-wave dynamics and X-ray irradiation
Simplified models of cooling SNRs in uniform media together with an idealized emission spectrum are used to investigate the X-ray irradiation of the surrounding gas. The radiative transfer of the emitted X-rays through both the dense cooling shell and the unshocked cloud is calculated, with a simplified treatment to allow for an ionized zone surrounding the SNR. Numerical results are presented for SN energy of 10 exp 51 ergs and ambient densities ranging from 100 to 1,000,000 cu cm. It is found that an appreciable fraction of the X-ray energy is absorbed in regions where the X-ray energy deposited per H nucleon is between 1 and 30 eV; if the gas is initially molecular, the X-ray irradiation will result in warm molecular gas in which endothermic chemical reactions may proceed, and from which there may be strong emission in rotation-vibration transitions of H2 and other molecular species.
Draine, B. T.↗
The rotational spectra of HOCO/plus/, HOCN, HN3, and HNCO from quantum mechanical calculations
Ab initio molecular orbital theory has been used to determine the equilibrium geometries, rotational constants, and rotational spectra of four isoelectronic molecules. Two of these, HOCO(plus) and HOCN, are candidate interstellar molecules. The other two, HNCO and HN3, have known rotational constants. Theoretical rotational constants and spectra for the two unknown species were corrected with the mean experimental to theoretical ratios from the two known species. This procedure resulted in predicted frequencies of 83.75 plus or minus 0.2 GHz for the 4(04) to 3(03) transition in HOCN and 85.08 plus or minus 0.2 GHz for the same transition in HOCO(plus). These are the central lines of triplets whose other members are the 4(14) to 3(13) and 4(13) to 3(12) transitions. The triplet splittings were predicted to be 0.36 plus or minus 0.01 GHz for HOCN and 0.33 plus or minus 0.01 GHz for HOCO(plus). These results indicate that HOCO(plus) is a better candidate for the source of a series of lines reported by Thaddeus, Guelin, and Linke than is HOCN.
Defrees, D. J.↗
Molecular collisions. XIX - The distorted wave approximation to atom-rigid symmetric top rotational excitation.
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Russell, D.↗
Molecular structure determination: Equilibrium structure of pyrimidine (m-C 4 H 4 N 2 ) from rotational spectroscopy (reSE) and high-level ab initio calculation (re) agree within the uncertainty of experimental measurement
The pure rotational spectrum of pyrimidine (m-C 4 H 4 N 2 ), the meta-substituted dinitrogen analog of benzene, has been studied in the millimeter-wave region from 235 GHz to 360 GHz. The rotational spectrum of the ground vibrational state has been assigned and fit to yield accurate rotational and distortion constants. Over 1700 distinct transitions were identified for the normal isotopologue in its ground vibrational state and least-squares fit to a partial sextic S-reduced Hamiltonian. Transitions for all four singly substituted 13 C and 15 N isotopologues were observed at natural abundance and were likewise fit. Deuterium-enriched samples of pyrimidine were synthesized, giving access to all eleven possible deuterium-substituted isotopologues, ten of which were previously unreported. Experimental values of rotational constants and computed values of vibration–rotation interaction constants and electron-mass corrections were used to determine semi-experimental equilibrium structures (r e SE ) of pyrimidine. The r e SE structure obtained using coupled-cluster with single, double, and perturbative triple excitations [CCSD(T)] corrections shows exceptional agreement with the re structure computed at the CCSD(T)/cc-pCV5Z level (≤0.0002 Å in bond distance and ≤0.03° in bond angle). Of the various computational methods examined, CCSD(T)/cc-pCV5Z is the only method for which the computed value of each geometric parameter lies within the statistical experimental uncertainty (2σ) of the corresponding semi-experimental coordinate. The exceptionally high accuracy and precision of the structure determination is a consequence of the large number of isotopologues measured, the precision and extent of the experimental frequency measurements, and the sophisticated theoretical treatment of the effects of vibration–rotation coupling and electron mass. Taken together, these demanding experimental and computational studies establish the capabilities of modern structural analysis for a prototypical monocyclic aromatic compound.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Ultrafast temporal phase-resolved nonlinear optical spectroscopy in the molecular frame
In an ultrafast nonlinear optical interaction, the electric field of the emitted nonlinear signal provides direct access to the induced nonlinear transient polarization or transient currents and thus carries signatures of ultrafast dynamics in a medium. Measurement of the electric field of such signals offers sensitive observables to track ultrafast electron dynamics in various systems. In this work, we resolve the real-time phase of the electric field of a femtosecond third-order nonlinear optical signal in the molecular frame. The electric field emitted from impulsively pre-aligned gas-phase molecules at room temperature, in a degenerate four-wave mixing scheme, is measured using a spectral interferometry technique. The nonlinear signal is measured around a rotational revival to extract its molecular-frame angle dependence from pump-probe time-delay scans. By comparing these measurements for two linear molecules, carbon dioxide and nitrogen, we show that the measured second-order phase parameter (temporal chirp) of the signal is sensitive to the valence electronic symmetry of the molecules, whereas the amplitude of the signal does not show such sensitivity. We compare measurements to theoretical calculations of the chirp observable in the molecular frame. This work is an important step towards using electric field measurements in nonlinear optical spectroscopy to study ultrafast dynamics of electronically excited molecules in the molecular frame.
47 OTHER INSTRUMENTATION↗
An upper limit to the acetylene abundance toward BN in the orion molecular cloud
A search for the acetylene (C2H2) nu3 infrared vibration-rotation absorption near 3 microns toward the Becklin-Neugebauer source in the Orion molecular cloud is reported. The relative abundance of C2H2/CO in the quiescent gas is less than 0.003.
Knacke, R. F.↗
Effect of rotational and vibrational excitation on interaction of diatomic molecules
A general and computationally efficient approach evaluating the central-force potentials for interaction of rotationally and vibrationally excited molecules and molecular ions is presented. Examples of numerical calculations are given for interactions of diatomic systems (H2, N2 and O2) in ground electronic states. The approach can be applied in straightforward way to interaction of atoms and atomic ions with diatomic molecules in arbitrary rotational-vibrational states.
Kunc, Joseph A.↗