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1

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Photodissociation of ClNO in the S1 state: A quantum-mechanical ab initio study (1990)

Schinke, Reinhard ; Nonella, Marco ; Suter, Hans Ulrich ; [et al.]

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 93 (1990), S. 1098-1106

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ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: We investigated the photodissociation of ClNO via the S1 electronic state using a three-dimensional (3D) ab initio potential-energy surface (PES). The dissociation is found to be fast and direct. In the Franck–Condon (FC) region the slope of the potential along the dissociation path is relatively small giving rise to narrow partial absorption peaks. The total absorption spectrum therefore exhibits a broad vibrational structure which is in perfect agreement with recent measurements. The vibrational excitation of the NO fragment is small and can be qualitatively described within the adiabatic approximation. It is found to be very sensitive to the vibrational FC factor in the transition region. The rotational state distribution of NO is highly inverted with a peak around j=30. It is readily explained by the rotational reflection principle. The experimental results are satisfactorily reproduced by our calculations which underlines the overall quality of the calculated PES. Minor adjustments are necessary, however, to quantitatively reproduce the vibrational branching ratio.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.459173

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2

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Diffuse vibrational structures in photoabsorption spectra: A comparison of CH3ONO and CH3SNO using two-dimensional ab initio potential energy surfaces (1989)

Schinke, Reinhard ; Hennig, Steffen ; Untch, Agathe ; [et al.]

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 91 (1989), S. 2016-2029

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ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: We investigated the photodissociation of methyl nitrite (CH3 ONO) and methyl thionitrite (CH3 SNO) within the first absorption band (S1 ←S0 ). The calculations were based on a two-dimensional model including the O–NO/S–NO and N=O bond distances as active coordinates. The S1 -potential energy surfaces were calculated with quantum chemical methods and the dynamical calculations were performed exactly within the time-independent approach. The main emphasis is on the origin of diffuse vibrational structure in the photoabsorption spectrum of both molecules. A low potential barrier of 0.086 eV along the O–NO dissociation coordinate in CH3 ONO prevents immediate dissociation and leads to an initial state dependent lifetime for the excited complex of 100–250 fs corresponding to 3–8 NO vibrational periods. CH3 ONO decays nonadiabatically via vibrational predissociation. The absorption spectrum of CH3 ONO is dominated by narrow Feshbach-like scattering resonances which can be characterized by two quantum numbers, m and n*: m=0 and 1 specifies the quanta of excitation in the O–NO bond and n*=0,1,2,... specifies the excited vibrational level of the N=O bond. The potential barrier is absent in CH3 SNO and the dissociation is direct on the time scale of about 10 fs corresponding to only one third of a NO vibrational period. Nevertheless, the absorption spectrum exhibits diffuse vibrational structures. The shape of the individual absorption peaks is determined by the classical Franck–Condon reflection principle. The dissociation of CH3 SNO is primarily adiabatic which leads to a pronounced energy dependence of the final NO vibrational state distribution. The diffuse structures originate in both cases from excitation of the NO stretching vibration. In order to make contact with time-dependent theory we calculated the autocorrelation function of the time-dependent wave function by inverse Fourier transformation of the energy-dependent spectra. The agreement with available experimental data for both molecules is quite satisfactory. This includes the energy spacing of the vibrational structure, the overall shape of the absorption spectrum, and thelifetime of the excited complex.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.457061

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3

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Photodissociation of CH3ONO in the first absorption band: A three-dimensional classical trajectory study (1989)

Nonella, Marco ; Huber, J. Robert ; Untch, Agathe ; [et al.]

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 91 (1989), S. 194-204

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ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: The photodissociation of cis-CH3 ONO following excitation into the first absorption band near 350 nm is investigated by means of classical trajectories and an ab initio potential energy surface. The calculations include the O–N coordinate, the N=O coordinate, and the ONO bending angle as variables whilst the internal degrees of freedom of the CH3 O moiety are kept fixed. The calculated lifetimes range from 120 to 410 femtoseconds for excitation of the n*=4 to n*=0 vibrational states of the terminal NO group in the intermediate complex. They agree well with the lifetimes estimated from the anisotropy parameter β. The ONO bending degree of freedom has only a small effect on the lifetime of the complex. The final vibrational state (n) distribution of the NO fragment exhibits a systematic energy dependence which manifests itself in a propensity for the excitation of level n=n*−1 that is in excellent agreement with the measurement. Two-dimensional calculations for a fixed ONO bending angle cannot satisfactorily reproduce these experimental findings. The rotational state distributions are highly inverted with maxima around j∼30–35 depending slightly on the initial state (n*) and the final state (n) of NO. The overall agreement with the measured distributions is satisfactory. The results of this study emphasize the importance of the bending degree of freedom in the dissociation of CH3 ONO and by revealing the interplay of the three active vibrational modes they provide a detailed picture of the predissociation mechanism in a polyatomic molecule.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.457663

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4

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Photodissociation dynamics of methylnitrite (CH3O–NO) in the 300–400 nm range: An ab initio quantum mechanical study (1987)

Hennig, Steffen ; Engel, Volker ; Schinke, Reinhard ; [et al.]

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 87 (1987), S. 3522-3529

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ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: We report the results of a two-dimensional, quantal study of the photodissociation of CH3O–NO within the first continuum (S0→S1, 300–400 nm) taking into account only the O–N and the N=O separations. The S1 potential energy surface is taken from recent ab initio calculations. The calculated absorption spectrum consists of two band progressions of narrow resonance lines with widths of ∼0.3 and ∼5 meV, respectively. These resonances can be associated with excitation of the O–N bond (m=0,1) and excitation of the N=O chromophore (n*=0,1,2,...). The intensities of the m=1 band are negligibly small compared to those of the m=0 band. The decay mechanism in the two cases is different: The m=0 resonances decay primarily via vibrational predissociation, i.e., a nonadiabatic transition from n* to n*−1, and yield NO products with a preferential population of the (n*−1) level. The m=1 resonances decay mainly via tunneling through a potential barrier yielding preferentially NO products in state n*. Several of the theoretical results agree qualitatively (ratio of peak intensities) or even quantitatively (energy spacing between peaks) with the measurements. Most important, however, is the good agreement found for the vibrational NO distributions at several excitation wavelengths of the parent, which reveals that vibrational predissociation within the S1 state is the main decay mechanism.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.452997

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5

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A quantum chemical investigation of structures, vibrational spectra and electron affinities of the radicals of quinone model compounds (1998)

Nonella, Marco

Springer

Photosynthesis research 55 (1998), S. 253-259

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ISSN: 1573-5079

Keywords: Density Functional Theory ; 2-methoxy-1 ; 4-benzoquinone ; 1 ; 4-naphthoquinone ; NormalCoordinate Analysis

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract In the present study, the first quantum chemical calculations of structures and vibrational spectra of radicals of 1,4-naphthoquinone and 2-methoxy-1,4-benzoquinone that account for electron correlation are presented. In the case of 1,4-naphthoquinone a good agreement between calculated vibrational frequencies and 18O-shifts of the 1,4-naphthoquinone radical (protonated radical anion) with experimental data of a species detected after irradiation of vitamin K1 in solution is found. Our calculations, thus, support the previous assignment. In the case of 2-methoxy-1,4-benzoquinone we have localized the stable conformations with respect to the orientation of the methoxy group and we have determine the harmonic force fields for these structures. Our calculation suggest that, while the frequencies of the two conformers are similar, the 18O-shift of the most intensive absorptions in the spectral region between 1400 and 1700 cm−1 of the two conformers differ significantly and might serve as a tool to distinguish between the two conformers. The applied DFT method is shown to predict electron affinities which are systematically underestimated by 10%.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1005935720437

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6

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Site-specific isotope labeling demonstrates a large mesomeric resonance effect of the methoxy groups on the carbonyl frequency in ubiquinones (1998)

Boullais, Claude ; Nabedryk, Eliane ; Burie, Jean-René ; [et al.]

Springer

Photosynthesis research 55 (1998), S. 247-252

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ISSN: 1573-5079

Keywords: infrared ; isotope labeling ; mesomeric resonance ; quinone

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract The splitting of the carbonyl infrared bands of 2-methoxy-1,4-benzoquinone in solution can be related to a mesomeric resonance phenomenon leading to a conformation of the O-CH3 bond coplanar to the quinone ring. The delocalization of the electron density induces a frequency downshift of the C4=O carbonyl compared to 1,4-benzoquinone. This in turns decouples the two carbonyls leading to an upshift of the C1=O vibration. Using selective 13C-labeling of Q0 (2,3-dimethoxy-5-methyl-1,4-benzoquinone), we show that the effect of mesomeric resonance is an essential determinant of the carbonyl frequencies of ubiquinone in solution.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1005979817422

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7

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HNO, an Intermediate in (Light-induced) Rearrangement Reactions of Nitrosooxy Compounds and Nitrosamines (1984)

Müller, René-Pierre ; Murata, Shigeo ; Nonella, Marco ; [et al.]

New York, NY : Wiley-Blackwell

Helvetica Chimica Acta 67 (1984), S. 953-958

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ISSN: 0018-019X

Keywords: Chemistry ; Organic Chemistry

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology

Notes: IR-spectroscopic investigations of light-induced rearrangement reactions of nitrosooxymethane (CH3ONO3), nitrosooxyethane (CH3CH2ONO) and N,N-dimethylnitrosamine ((CH3)2NNO) in low-temperature rare-gas matrices have established that these molecules are transformed in two photolysis steps to the previously unknown C-nitroso compounds nitrosomethanol (CH2(OH)(NO)), 1-nitrosoethanol (CH3CH(OH)(NO)), and methyl(nitrosomethyl)amine CH2(NO)(NH)(CH3). Evidence for a similar rearrangement reaction has been advanced for N-Nitrosopyrrolidine which is converted to C-nitrosopyrrolidine . The matrix-isolation technique in combination with wavelength-selective irradiation allowed to trap and characterize an intermediate of rearrangement which revealed to be nitroxyl (HNO) complex (CH2…HNO, CH3CHO…HNO, CH3N = CH2…HNO, and ). Since these findings have a close resemblance with rearrangement reactions of more complex nitrosooxy compounds, nitrosamines, or nitrosohydrazines used in organic synthesis, it is suggested that also in these reactions nitroxyl is present as an intermediate species.

Additional Material: 3 Tab.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1002/hlca.19840670406

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8

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Effect of charge distribution on electrostatic chromophore - protein interactions in Bacteriorhodopsin (1997)

Nonella, Marco

New York, NY [u.a.] : Wiley-Blackwell

Journal of Computational Chemistry 18 (1997), S. 677-693

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ISSN: 0192-8651

Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology , Computer Science

Notes: Charge distributions of a protonated and unprotonated Schiff base model compound are determined using different quantum chemical methods. After fitting the model molecule onto the protonated retinal Schiff base in Bacteriorhodopsin, electrostatic interaction energies between the model molecule and protein are calculated. Interaction energies as well as the calculated pK1/2 values of the model molecule are shown to depend considerably on the chosen charge distribution. Electrostatic potential derived partial charges determined at different ab initio levels reveal interaction energies between the model molecule and nearby residues such as ARG-82, ASP-85, and ASP-212, which are relatively method independent. Consequently, such charge distributions also result in pK1/2 values for the model molecule that are very similar. Larger deviations in the electrostatic interaction energies, however, are found in the case of charge distributions derived according to the Mulliken population analysis. Nevertheless, some sets of Mulliken derived partial charges predicted pK1/2 values for the model molecule that are close to those determined with electrostatic potential derived partial charges. This agreement, however, is only achieved because the individual errors of the contributing terms are approximately compensated. The use of the extended atom model is shown to be problematic. Although potential derived charges can correctly describe electrostatic interaction energies, they fail to predict pK1/2 values. On the basis of the present investigation a new set of partial charges for the protonated and unprotonated retinal Schiff base is proposed to be used in molecular dynamics simulations and electrostatics calculations. © 1997 by John Wiley & Sons, Inc.

Additional Material: 4 Ill.

Type of Medium: Electronic Resource

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