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  • 11
    Electronic Resource
    Electronic Resource
    Charge-transfer interactions between transition metal hexafluorides and xenon (1978)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 100 (1978), S. 483-485 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00470a019
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  • 12
    Electronic Resource
    Electronic Resource
    Benzene clustered with N2, CO2, and CO: Energy levels, vibrational structure, and nucleation (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 1309-1321 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Two-color time-of-flight mass spectroscopy is employed to study the van der Waals (vdW) clusters of benzene(N2)n (n≤8), benzene(CO2)n (n≤7), and benzene(CO)n (n=1,2) created in a supersonic molecular jet. Potential energy calculations of cluster geometries, normal coordinate analysis of vdW vibrational modes, and calculations of the internal rotational transitions are employed for the assignment of the benzene(solvent)1 cluster spectra in the 000 and 610 regions of the benzene 1B2u←1A1g transition. The respective vibronic and rotational selection rules for these clusters are determined based on the appropriate point groups and molecular symmetry groups of the clusters. Good agreement between the calculated and experimental spectra is obtained with regard to the vdW vibrational and internal rotational modes. The solvent molecules rotate nearly freely with respect to benzene about the benzene–solvent bond axis in the benzene(solvent)1 clusters. In the excited state a small ∼20 cm−1 barrier to rotation is encountered. Studies of larger clusters (n〉2) reveal a broad red shifted single origin in the 610 spectra. A linearly increasing cluster energy shift is observed as a function of cluster size. The cluster energy shifts are not saturated by one solvent molecule on each side of the aromatic ring; several solvent molecules effectively interact with the solute π electronic cloud. Both homogeneous and inhomogeneous nucleation take place for the clusters studied depending on the ratio of the solvent–solvent binding energy to the cluster binding energy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455182
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  • 13
    Electronic Resource
    Electronic Resource
    Supersonic molecular jet spectroscopy of ethylbenzene, the ethyltoluenes, and the diethylbenzenes (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 3269-3275 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Time-of-flight mass spectra are presented for the S1←S0 origin region of jet-cooled 1,2-, 1,3-, and 1,4-diethylbenzene, and 2-, 3-, and 4-ethyltoluene. The spectra for the diethylbenzenes exhibit two origins which are assigned to syn and anti conformations of the ethyl groups relative to the aromatic ring. The existence of two origins in the 1,3-diethylbenzene spectrum, and only one in the 3-ethyltoluene spectrum, strongly implies that the stable orientation of the ethyl groups is with the β-carbon atom of the ethyl group projecting perpendicular to the plane of the aromatic ring. The size and shape of the potential barrier to rotation of the ring methyl group is obtained by treating the methyl group as a one-dimensional rigid rotor and fitting the calculated energy levels to observed features in the spectra. The results (for the para isomer B=5.20 cm−1, V6=31.00 cm−1; for the meta isomer, B=5.40 cm−1, V3=78.00 cm−1; and for the ortho isomer, B=5.50 cm−1, V3=89.00 cm−1) indicate that the methyl group experiences an increased barrier to rotation in the order para〈meta〈ortho isomer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453019
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  • 14
    Electronic Resource
    Electronic Resource
    Spectroscopic studies of cryogenic fluids: Benzene in nitrogen (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 4783-4789 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Energy shifts and bandwidths for the 1B2u←1A1g optical absorption of benzene in supercritical nitrogen are presented as a function of pressure, temperature, and density. The pressure and density dependence of energy shifts of room temperature emission of benzene in nitrogen fluid is also reported. Both absorption and emission spectra exhibit shifts to lower energy as a function of density, whereas almost no spectral shifts are observed if the density is kept constant and temperature and pressure varied simultaneously. Thus, density is the fundamental microscopic parameter for energy shifts of optical transitions in supercritical nitrogen. This result is analogous to the findings for the liquid benzene/propane system and can be interpreted qualitatively in terms of changes occurring in the intermolecular potential; however, in the benzene/supercritical nitrogen system an additional small density independent temperature effect on the transition energy has been identified. Experimental results are compared to dielectric (Onsager–Böttcher and Wertheim) and microscopic quantum statistical mechanical (Schweizer–Chandler) theories of solvent effects on solute electronic spectra. Reasonably good agreement between experiment and theory is found. The results demonstrate that liquid state theory can be used to describe the supercritical nitrogen fluid.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452700
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  • 15
    Electronic Resource
    Electronic Resource
    Vibrational dynamics of aniline(Ar)1 and aniline(CH4)1 clusters (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 5268-5277 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The first excited electronic state (S1) vibrational dynamics of aniline(Ar)1 and aniline(CH4)1 van der Waals (vdW) clusters have been studied using molecular jet and time resolved emission spectroscopic techniques. The rates of intramolecular vibrational energy redistribution (IVR) and vibrational predissociation (VP) as functions of vibrational energy are reported for both clusters. For vibrational energy in excess of the cluster binding energy, both clusters are observed to dissociate. The dispersed emission spectra of these clusters demonstrate that aniline(Ar)1 dissociates to all energetically accessible bare molecule states and that aniline(CH4)1 dissociates selectively to only the bare molecule vibrationless state. The emission kinetics show that in the aniline(Ar)1 case, the initially excited states have nanosecond lifetimes, and intermediate cluster states have very short lifetimes. In contrast, the initially excited aniline(CH4)1 states and other intermediate vibrationally excited cluster states are very short lived (〈100 ps), and the intermediate cluster 00 state is observed. These results can be understood semiquantitatively in terms of an overall serial IVR/VP mechanism which consists of the following: (1) the rates of chromophore to vdW mode IVR are given by Fermi's golden rule, and the density of vdW vibrational states is the most important factor in determining the relative [aniline(Ar)1 vs aniline(CH4)1] rates of IVR; (2) IVR among the vdW modes is rapid; and (3) VP rates can be calculated by a restricted vdW mode phase space Rice–Ramsberger–Kassel–Marcus theory. Since the density of vdW states is three orders of magnitude greater for aniline(CH4)1 than aniline(Ar)1 at 700 cm−1, the model predicts that IVR is slow and rate limiting in aniline(Ar)1, whereas VP is slow and rate limiting in aniline(CH4)1. The agreement of these predictions with the experimental results is very good and is discussed in detail.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457572
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  • 16
    Electronic Resource
    Electronic Resource
    Conformational changes upon S1←S0 excitation in 4-dimethylaminobenzonitrile and some of its chemical analogs (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 3994-3999 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: One-color time-of-flight mass spectra (mass resolved excitation spectra) for jet-cooled 4-dimethylaminobenzonitrile (4-DMABN) and some of its chemical analogs, dimethylaniline (DMA), 3-dimethylaminobenzonitrile (3-DMABN), N, N-dimethyl-4-(trifluoromethyl)aniline (4-CF3-DMA), and 4-(d6-dimethylamino)benzonitrile (4-d6-DMABN), are presented and analyzed. Near the origin of the S1←S0 transition the low frequency modes can be assigned to motions of the dimethylamino group for this series of molecules. The inversion motion of the dimethylamino group and the dimethylamino group torsion about the Cipso–N bond (the twist coordinate) in S1 give rise to the most prominent peaks in this spectrum. The potential parameters for the twist coordinate of 4-DMABN and DMA are quite similar in S1: B=0.546, V2=175, and V4=525 cm−1 for 4-DMABN and B=0.546, V2=175, and V4=515 cm−1 for DMA. The V2 and V4 terms are slightly larger for 3-DMABN and 4-CF3-DMA. The inversion motion is also similar for these molecules but is more anharmonic for the para-substituted dimethylanilines, 4-DMABN and 4-CF3-DMA, than for the meta and unsubstituted molecules. A Franck–Condon intensity analysis for the dimethylamino twist in these molecules suggests that this group in 4-DMABN is displaced in the excited state by ∼30° with respect to its planar orientation in the ground state. In both solutions and monosolvate clusters of 4-DMABN with polar aprotic solvents, a low lying charge transfer (CT) state is identified in addition to the usual ππ* excited state of the bare molecule. The relation between the bare molecule 4-DMABN twisting displacement upon excitation and the low lying CT state is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455809
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  • 17
    Electronic Resource
    Electronic Resource
    Chemical reactions in isolated clusters: Excited state electron transfer in 3- and 4-dimethylaminobenzonitrile (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 871-878 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Two-color time-of-flight mass spectra of 3- and 4-dimethylaminobenzonitrile (3- and 4-DMABN) bare molecules and clusters with methane, water, acetone, dichloromethane, and acetonitrile are reported and discussed. The clusters and molecules are isolated and cooled in a supersonic expansion. Both 3- and 4-DMABN bare molecules display significant changes in geometry, associated with rotation–inversion coordinates of the dimethylamino group, upon excitation from the ground electronic state S0 to the first excited singlet state S1. Cluster spectra for the monosolvates [CH4, H2O, (CH3)2CO, CH2Cl2, CH3CN] of 3- and 4-DMABN evidence two general types of behavior. (1) Cluster spectra have both red and blue shifts from their respective bare molecule origins which are relatively small (in general less than 200 cm−1). These cluster spectra are nearly identical with the bare molecule spectra; the solvation process seems to have little effect on the DMABN molecule, especially the –N(CH3)2 moiety, for these clusters or cluster states. (2) Cluster spectra have shifts that are large (∼500–1000 cm−1) and to low energy of the bare molecule spectra. These cluster spectra are composed of both sharp and broad features which bear little resemblance to those observed in the respective bare DMABN molecule spectra. Results of calculations of cluster geometry suggest that thedifferent cluster spectra may be associated with clusters of different geometry. These data are interpreted in terms of solution behavior of 3- and 4-DMABN. The relationship between the twisted intramolecular charge transfer (TICT) state model proposed for 4-DMABN in dipolar aprotic solvents and these cluster results is explored.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454166
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  • 18
    Electronic Resource
    Electronic Resource
    Geometry and torsional motion of biphenyl in the ground and first excited singlet state (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 7337-7347 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The lowest excited singlet state of biphenyl (BP) and a number of its isotopically and chemically substituted analogs have been studied by supersonic jet laser spectroscopy. The symmetry species of this excited state in BP can be classified as B+2u in the G16 extended molecular symmetry group G16 (EM). The symmetry-allowed origin of the biphenyl -h10 S1←S0 electronic transition occurs at 35 268 cm−1. The frequency of the torsional motion in S1 is determined to be ∼65 cm−1. The potential parameters for this motion in S1 are V2=1195 cm−1, V4=−190 cm−1, and V6=18 cm−1. The torsional motion for the ground state (∼50 cm−1) can be described by V2=50 cm−1 and V4=−148 cm−1. The change in the dihedral angle between the two benzene rings in BP upon S0 to S1 excitation is determined to be ∼44° based on a Franck–Condon factor calculation. Several fundamentals of the molecular vibrations are assigned in the S1 state. The exciton interaction between the coupled benzene rings in biphenyl is suggested to be large (〉103 cm−1).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454345
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  • 19
    Electronic Resource
    Electronic Resource
    Spectroscopic studies of cryogenic fluids: Benzene in argon and helium (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 2457-2465 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Energy shifts and bandwidths of the 610 vibronic feature of the 1B2u←1A1g optical absorption spectrum of benzene dissolved in supercritical argon and helium, and in liquid argon are reported as a function of pressure, temperature, and density. Benzene/Ar solutions display red shifts of the 610 transition with increasing density but the dependence is found to be nonlinear at high densities. Benzene/He solutions evidence blue shifts of the 610 transition as a function of increasing density which also becomes nonlinear at high densities. Only small spectral shifts are recorded if the density is kept constant and pressure and temperature are varied simultaneously. In addition, a small density independent temperature effect on the transition energy shift is identified. Experimental results are compared to dielectric (Onsager–Böttcher and Wertheim) and quantum statistical mechanical (Schweizer–Chandler) theories of solvent effects on solute absorption energy. Reasonably good agreement between experiment and theory is found only for the benzene/Ar system at relatively low densities. The theory fails to predict energy shifts for both the benzene/He and high density benzene/Ar systems. This result is different from the findings for the benzene/N2 and benzene/C3H8 solutions and can be interpreted qualitatively in terms of competition between dispersive attractive and repulsive interactions as a function of density. The failure of the theory to describe these transition energy shifts is attributed to the omission of explicit repulsive interactions terms in the theoretical models employed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453086
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  • 20
    Electronic Resource
    Electronic Resource
    van der Waals clusters of pyridazine and isoquinoline: The effect of solvation on chromophore electronic structure (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 6707-6716 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: van der Waals clusters of pyridazine and isoquinoline with CH4, NH3, H2O, and CH3OH are generated in a supersonic molecular jet expansion and investigated by two-color time-of-flight mass spectroscopy. As is the case for the other diazine systems, no spectra could be observed for pyridazine (H2O)n or (CH3OH)n clusters. Both chromophore molecules are reported to have close lying, vibronically coupled S1 and S2 excited states: nπ* for pyridazine and nπ* (S1) and ππ* (S2) for isoquinoline. Cluster spectra for pyridazine methane and ammonia clusters do not favor the presence of two nπ* transitions in the S1←S0 transition region but rather suggest that the "S2 origin'' is a vibronic feature of the S1←S0 transition. Isoquinoline clusters that are only weakly or not at all hydrogen bonded (CH4 and NH3) display a complicated spectrum indicative of S1 (nπ*)–S2 (ππ*) vibronic coupling and not the usual shifted isolated molecular spectrum. Isoquinoline clusters with substantial hydrogen bonding (H2O and CH3OH) display relatively simple spectra indicative of only a single electronic transition S2 (ππ*)←S0 in the region and no interstate vibronic coupling. These results are compared and contrasted with each other and the spectra of the other diazine clusters. Potential energy calculations are also employed to help understand the clustering in these systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452369
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