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  • Articles  (18)
  • American Institute of Physics (AIP)  (18)
  • 2000-2004  (2)
  • 1990-1994  (16)
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  • Articles  (18)
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  • 1
    Electronic Resource
    Electronic Resource
    Potential energy surfaces of substituted anilines: Conformational energies, deuteration effects, internal rotation, and torsional motion (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 7889-7901 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Mass resolved excitation spectra (MRES) are presented for a series of substituted anilines including 2- and 3-methylaniline, 2- and 3-ethylaniline, 2-aminobenzyl amine, and 2-aminobenzyl alcohol. The observed spectra show the following phenomena: nearly free internal rotation of the methyl substituent in the S1 state; long vibrational progressions attributed to C–C, C–N, and C–O side chain torsional motion; an inequivalence of the two amino hydrogens for both ring and side chain amino groups as determined from the spectra of deuterated species; and the existence of two conformers for 2-aminobenzyl alcohol. Semiempirical and ab initio calculations are performed on these systems to aid in the analysis of the potential energy surfaces and in the interpretation of the experimental results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463464
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  • 2
    Electronic Resource
    Electronic Resource
    Minimum energy conformation of ortho-xylene in its ground and first excited electronic states (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 8130-8136 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The geometry of ortho-xylene is studied through supersonic jet cooling and one color mass resolved excitation spectroscopy. By examining the S1←S0 transition origin region of various (d0–d2) methyl deuterated o-xylene species, the conformation of the two methyl groups in S0 and S1 can be determined. A comparison between the predicted and experimentally observed number and intensity of origin features for the various partially deuterated o-xylenes shows that two highly symmetric methyl group structures are possible, each structure having C2V point group symmetry—the antiplanar conformation (A1), in which τ1(C2–C1–Cα–Hα)=180°; τ2(C1–C2–Cα'–Hα')=180°; and the syn, planar conformation (A2) in which τ1=τ2=0°. The experimentally determined structures are consistent with ab initio calculations and microwave studies which predict the anticonformation to be most stable. Spectroscopic data, in conjunction with further ab initio calculations, are used to investigate the ground and excited state potential energy surfaces. In addition, a repulsive, intramolecular, nonbonded interaction between the two methyl groups is identified through an empirical potential energy calculation to be the most important interaction defining the lowest energy structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463434
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  • 3
    Electronic Resource
    Electronic Resource
    Vibrational dynamics of aniline (N2)1 clusters in their first excited singlet state (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 4904-4910 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The first excited singlet state S1 vibrational dynamics of aniline(N2)1 clusters are studied and compared to previous results on aniline(CH4)1 and aniline(Ar)1. Intramolecular vibrational energy redistribution (IVR) and vibrational predissociation (VP) rates fall between the two extremes of the CH4 (fast IVR, slow VP) and Ar (slow IVR, fast VP) cluster results as is predicted by a serial IVR/VP model using Fermi's golden rule to describe IVR processes and a restricted Rice–Ramsperger–Kassel–Marcus (RRKM) theory to describe unimolecular VP rates. The density of states is the most important factor determining the rates. Two product states, 00 and 10b1, of bare aniline and one intermediate state ∼(00) in the overall IVR/VP process are observed and time resolved measurements are obtained for the 000 and ∼(000) transitions. The results are modeled with the serial mechanism described above.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462780
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  • 4
    Electronic Resource
    Electronic Resource
    Normal mode analysis of van der Waals vibrations (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 1577-1587 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Two algorithms are presented for calculation of the van der Waals modes of weakly bound clusters. Both methods rely on the harmonic normal mode approximation and a chosen intermolecular potential. These calculational techniques differ specifically in the form of the force field employed: one method uses the total (both intra- and intermolecular) force field for the cluster and the other uses only the intermolecular force field. Both methods require rather elaborate coordinate transformation and their first and second partial derivatives; these are provided in detail. The two calculations generate eigenvalues and eigenvectors that are in complete agreement with one another for a given potential. The methods insure that the van der Waals modes are calculated at the proper cluster equilibrium configuration for which all torques and forces on molecules and/or atoms are effectively zero. Examples are presented for (H2O)n (n=2,...,7), benzene clustered with water, methane, and ammonia, and a number of different intermolecular potentials. Some of the observed heterogeneous cluster van der Waals modes are reassigned in light of these new results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461072
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  • 5
    Electronic Resource
    Electronic Resource
    Benzyl alcohol–water and benzyl alcohol–ammonia clusters: Ion fragmentation and chemistry (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 7383-7391 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Benzyl alcohol/ammonia, α,α-dimethylbenzyl alcohol/ammonia, and benzyl alcohol/water cluster ion fragmentation and chemistry are studied for isolated cold clusters by means of one and two-color mass resolved excitation spectroscopy, nozzle/laser timing delay, and deuteration experiments. Experiments lead to an identification of parent clusters for all fragment ion clusters observed. Three types of cluster ion fragmentation are observed for these systems: dissociation−solu+(solv)n→solu+(solv)k+m solv; acid-base chemistry−ArCH2OH+(B)n→ArCH2O(B)k+BmH+; and (benzyl) radical chemistry−ArCH2OH+(B)n→ArC(overdot)HOH(B)k+BmH+, ArCD2OH+(B)n→ArCDHOH+(B)k+BmB−d2 and ArCMe2OH+(B)n→ArC(overdot)MeOH+(B)k+BmM(overdot)e. Fragmentation reactions depend on cluster size, structure, and (weakly) on the vibrational energy deposited in the ion. Specifically, for benzyl alcohol+(NH3)1 only cluster radical chemistry and dissociation take place, while for higher order clusters, the acid-base reaction rate increases and this reaction becomes a major fragmentation pathway for benzyl alcohol+(NH3)4. For the benzyl alcohol(H2O)n system, cluster radical chemistry is not observed with n=1, only a weak α-hydrogen transfer reaction is observed with n=2, and acid base chemistry is not observed for clusters of any size. Cluster dissociative fragmentation is also a function of cluster size; large water and ammonia clusters dissociate much more easily than do n=1 clusters. The possible mechanisms for these fragmentation patterns are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463510
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  • 6
    Electronic Resource
    Electronic Resource
    Reply to the Comment on: The torsional potential function of dimethylaminobenzonitrile and related compounds in their S1 states (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 6910-6910 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458925
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  • 7
    Electronic Resource
    Electronic Resource
    Excited-state proton transfer in 1-naphthol/ammonia clusters (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 3341-3347 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Excited-state proton transfer dynamics are reported for the 1-naphthol(NH3)n cluster system for n=3 and 4. Picosecond time- and mass-resolved pump (S1←S0)–probe (I←S1) experiments demonstrate the following results: (1) excited-state proton transfer occurs for n=3 and 4 clusters only; (2) for n=5 clusters the proton is transferred in the ground state and for n=2 clusters no proton transfer can be observed; (3) the proton transfer time in the n=3 cluster at the 000 transition is ca. 60 ps; (4) this time is reduced to ca. 40 ps and ca. 10 ps for 800 and 1400 cm−1 of vibrational energy in S1, respectively; (5) for the n=4 clusters these times are approximately 70, 70, and 30 ps, for 0, 800, and 1400 cm−1 of vibrational energy in S1, respectively; (6) both n=3 and 4 clusters exhibit a second low-amplitude decay component, which is about an order of magnitude slower than the initial decay; and (7) 1-naphthol-d1(ND3)n clusters have a greatly reduced rate constant for the excited-state proton transfer dynamics. These observations are well fit and explained by a simple statistical/barrier penetration model involving proton tunneling and the effect of van der Waals vibrations on the height and width of the barrier to proton transfer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462971
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  • 8
    Electronic Resource
    Electronic Resource
    The effect of solvation on molecular Rydberg states: Dioxane clustered with nonpolar solvents (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 2869-2880 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: One color 2+1 mass resolved excitation spectroscopy is employed to obtain molecular Rydberg 3s←n transition spectra of 1,4-dioxane clustered in a molecular beam with nine nonpolar solvents. The solvents are Ar, Kr, CH4, CD4, CF4, SiH4, Si(CH3)4, ethane, n-propane, cyclohexane-h12, and cyclohexane-d12. Spectral results are interpreted in terms of cluster size, isotope effects, and model calculations. A Lennard-Jones–Coulomb 6-12-1 potential is used to model the intermolecular interactions and predict minimum energy cluster geometries, cluster binding energies, and intermolecular force constants which are used to calculate van der Waals vibrational frequencies. The results show that for simple solvents (i.e., Ar, CH4) the calculations offer a simple interpretation of the observed spectra in terms of multiple cluster geometries with distinct transition energies; however, as the solvent becomes more complex, the cluster spectra also become more complex, and the number of calculated minimum energy cluster geometries increases. Complex spectra are interpreted as a distribution of cluster geometries with similar transition energies. For all of the clusters, the electronic origins are blue shifted with respect to the bare 1,4-dioxane origin. This observation is consistent with a model in which the excited state intermolecular potential becomes more repulsive due to the increased radial distribution of a nonbonding electron upon excitation into the 3s Rydberg state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463029
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  • 9
    Electronic Resource
    Electronic Resource
    Mass resolved excitation spectroscopy of radicals: Benzyl and phenylnitrene (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 6326-6329 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Two-color mass resolved excitation spectra are obtained for the benzyl and "phenylnitrene'' radicals. The spectrum previously assigned to the benzyl radical is generated by a species with mass 91 amu. This finding is consistent with the proposed C6H5C(overdot)H2 benzyl radical structure. The origin of this 1 2A2←1 2A1 transition lies at 21 997 cm−1. The ionization energy for the benzyl radical is ∼7.236 eV. The phenylnitrene radical spectrum is associated with a species of 90 amu. The phenylnitrene designation is not appropriate for this mass number: the suggested cyanocyclopentadienyl radical species (C5H4CN) is consistent with this mass. This radical has an ionization threshold of ∼9.05 eV. Lifetimes are reported for a number of the vibronic states of both radicals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461553
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  • 10
    Electronic Resource
    Electronic Resource
    Excited state proton transfer in the S1 state of 2-allylphenol, 2-propenylphenol, and 2-propylphenol and their van der Waals clusters with water and ammonia (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 3290-3301 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Excited state intramolecular and intermolecular proton transfer reactions in cold, isolated 2-allylphenol, 2-propenylphenol and 2-propylphenol, and their clusters with water and ammonia are investigated employing a combination of spectroscopic techniques (mass resolved excitation, threshold photoionization, dispersed emission), a semiempirical calculation (MOPAC 5) and a potential energy calculation of cluster structure. Threshold photoionization spectroscopy proves to be useful for the identification of molecular conformers in these systems but has mixed results for the identification of proton transfer in their clusters. The total collection of generated data suggests the following conclusions: (1) isolated, cold 2-allylphenol displays only one conformation which appears to have a significant stabilizing intramolecular interaction between the allyl group double bond and the hydroxyl group hydrogen atom; (2) 2-propenylphenol displays only one conformer; (3) 2-propylphenol has many conformations—probably more than five under the experimental conditions; (4) no evidence of intramolecular proton transfer can be found for these three isolated cold molecules; (5) no evidence for intermolecular proton transfer in water clusters has been found by any of the above techniques; and (6) evidence is found for intermolecular proton transfer in 2-allyl- and 2-propenylphenol(NH3)n, n≥3, in dispersed emission spectra. Dispersed emission spectra of 2-propylphenol(NH3)n n≥3 are too weak to yield conclusive evidence for intermolecular excited state proton transfer. Potential energy minimization calculations of cluster geometry suggest that the difference between water and ammonia cluster behavior with regard to proton transfer arises because water molecules hydrogen bond with the hydroxyl group (both OH⋅⋅⋅OH2 and HO⋅⋅⋅HOH) and each other while ammonia molecules are more evenly distributed over the entire molecular structure of the phenol moiety. Apparently, for efficient proton transfer to occur in clusters, the proton affinity of the solvent must be large and both the anion and the proton must be well solvated (stabilized) by the solvent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460835
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