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Fullerene C60 is used in a variety of industrial and consumer capacities. As part of a comprehensive evaluation of the toxicity of fullerene C60 by the National Toxicology Program, the disposition following intratracheal (IT) instillation and intravenous (IV) administration of 1 or 5 mg/kg b.wt. fullerene C60 was investigated in male Fischer 344 rats. Following IT instillation, fullerene C60 was detected in the lung as early as 0.5 h post-exposure with minimal clearance over the 168 h period; the concentration increased ≥20-fold with a 5-fold increase in the dose. Fullerene C60 was not detected in extrapulmonary tissues. Following IV administration, fullerene C60 was rapidly eliminated from the blood and was undetectable after 0.5 h post-administration. The highest tissue concentrations of fullerene C60 occurred in the liver, followed by the spleen, lung and kidney. Fullerene C60 was cleared slowly from the kidney and the lung with estimated half-lives of 24 and 139 h, respectively. The liver concentration of fullerene C60 did not change much with time; over 90% of the fullerene C60 remained there over the study duration up to 168 h. Fullerene C60 was also not detected in urine or feces. These data support the hypothesis that fullerene C60 accumulates in the body and therefore has the potential to induce detrimental health effects following exposure. [ABSTRACT FROM AUTHOR]

Intramolecular vibrational energy redistribution (IVR) is studied by picosecond time resolved stimulated emission pumping (TRSEP). This technique is used to obtain decays for 3 of the 19 previously studied vibronic levels in p-cyclohexylaniline. These TRSEP decays allow one to quantitatively measure the ratio of fast to slow fluorescence intensities in order to obtain accurate values for the number of coupled states. This data inspired us to take a closer look at the time decays which eventually led to the understanding of why the medium energy levels exhibit temporal behavior with fast initial decays and small damped quantum beats when large undamped quantum beats are expected. This paper demonstrates that the rotational state interactions are the cause for this interesting behavior. [ABSTRACT FROM AUTHOR]

This paper presents the results of a temperature dependence study of time resolved fluorescence depletion (TRFD) measurements of intramolecular vibrational energy redistribution in the molecule p-cyclohexylaniline. TRFD scans of five vibrational bands of p-cyclohexylaniline were taken at several molecular beam conditions corresponding to rotational temperatures in the range of 8–110 K. The results are attributed to two possible coupling mechanisms and are shown to be consistent with previous work. Although rotational effects are probably dominant, our data also indicate that excitation of low (40 cm-1) vibrations may contribute to enhanced relaxation. [ABSTRACT FROM AUTHOR]

This paper presents the results of the picosecond time-resolved study of intramolecular vibrational relaxation (IVR) in the molecule p-cyclohexylaniline. The results represent the second extensive study of a molecule using the technique which we have developed known as time-resolved fluorescence depletion (TRFD). Fluorescence depletion decays and dispersed fluorescence spectra of 19 S1 vibronic features are presented. The decays show a progression of dynamic behavior, including stationary behavior at low densities of states, quantum beating at intermediate densities, and fast decay of the initially prepared state at high state densities. The data allow us to assign IVR lifetimes which range from 250 ps at 820 cm-1 of excess vibrational energy to 2.2 ps at 2362 cm-1. Even at the highest frequencies we observe, the decays do not tend toward a simple exponential, but instead exhibit weak damped quantum beats. [ABSTRACT FROM AUTHOR]

The effects of rotation–torsion interactions on the rotational structure of torsional vibronic bands in an electronic spectrum are examined, and a computer program to calculate the relevant energies and transition intensities is described. Rotationally resolved type C bands in the 1nπ* spectrum of methylglyoxal are reported and interpreted. Since the torsional conformation of methylglyoxal differs in the two electronic states, a long progression of bands is observed, involving levels well below, near, and above the 190 cm-1 S1 torsional barrier. The rotation–torsion interaction increases rapidly towards the free rotor limit as the barrier is approached. Observed effects include energy shifts and the appearance of transitions forbidden by rigid rotor or torsional vibronic selection rules. [ABSTRACT FROM AUTHOR]

Stimulated emission pumping (SEP) spectroscopy has been used to investigate rovibrational level mixing in the ground singlet state of methyl glyoxal. A low resolution (0.35 cm-1) SEP survey spectrum allows accurate frequency assignments for 15 normal vibrations and seven hindered rotor levels. High resolution (0.05 cm-1) SEP spectra are reported for selected vibrational bands, including the fundamental vibrations of the symmetric carbonyl stretch and symmetric carbonyl bend. A van der Waals interaction between the neighboring carbonyl oxygen and methyl hydrogens is found to influence mixing of the carbonyl vibrations, affirming the results of previous studies. [ABSTRACT FROM AUTHOR]

This paper describes the experimental implementation and theory of a new technique for the time resolved study of intramolecular vibrational redistribution: time resolved fluorescence depletion (TRFD). Picosecond time resolution is obtained by using two pulses of identical wavelength and duration to create and then stimulate emission from a vibrational state in S1. Spontaneous emission intensity is measured as a function of delay between pulses. By monitoring the efficiency with which the second pulse stimulates emission, the evolution of the initial optically prepared state can be followed. A description of the apparatus built for these experiments is also presented. [ABSTRACT FROM AUTHOR]

This paper presents the results of the time-resolved study of intramolecular vibrational relaxation in the molecule fluorene. The results represent the first extensive study of a molecule using the technique which we have developed known as the time-resolved fluorescence depletion technique. Fluorescence depletion decays and dispersed fluorescence spectra of 19 vibronic features of fluorene are presented. The decays show a progression of dynamic behavior including stationary behavior at low densities of states, quantum beating at intermediate densities, and fast decay of the initially prepared state at high state densities. The data allow us to assign IVR lifetimes to several vibronic levels of fluorene from 27 ps at 1425 cm-1 of excess vibrational energy to ≤10 ps at ∼2000 cm-1. The degree of spectral congestion in the associated dispersed fluorescence spectra is shown to be related to the dynamic behavior of the vibronic features. In addition, the effects of intermolecular rotational coherences on the time-resolved fluorescence depletion decays of fluorene are explored. With these results we are able to confirm the assignments of the excited state rotational constants which we have made using rotational band contour simulations. [ABSTRACT FROM AUTHOR]

We have studied rovibrational state mixing in acetaldehyde using infrared laser induced fluorescence. Molecules are isolated and cooled in supersonic molecular beams, and irradiated in the C–H stretch fundamental region with an infrared optical parametric oscillator. Spectral resolution is provided with either a circular variable filter machine or a cryogenic Michelson interferometer. We have found evidence of several strong Fermi resonances between the aldehyde C–H stretch and a few overtones and combinations of lower frequency modes. In addition, there is substantial random state mixing in this region as evidenced by the average experimental dilution factor of 0.2. The dependence of the dilution factor on the average J excited by the laser shows that the extent of state mixing scales linearly with J. We have observed from dispersed fluorescence spectra that random rotational coupling occurs between different Kp states. Our previous statistical coupling model has been applied to the interpretation of the data, and its applicability is discussed. For the model calculation, the methyl torsion is specially treated as a very anharmonic mode in the eumeration of the zeroth order bath states. The average coupling width derived from the model calculation is 0.35 cm-1. The relative energy content apportioned among vibrational modes in the molecule following excitation is measured and is successfully explained with the model. [ABSTRACT FROM AUTHOR]

Infrared laser induced fluorescence has been used to probe the extent of state mixing, as well as its rotational dependence, in the C–H stretch fundamental region of norbornadiene in the electronic ground state. Both total and dispersed IR fluorescence were collected from molecules, cooled, and isolated in a molecular beam, after excitation with an infrared optical parametric oscillator. The dilution factor, which is inversely related to the number of coupled states, has been measured for four C–H stretch bands, and in addition, the rotational dependence of the dilution factor has been investigated by exciting different positions, or average J values, within a single vibrational band. The relative energy contents of various vibrational modes, whose fluorescence was observed, have also been determined. An approximate average coupling width of 0.05 cm-1 can be derived from the dilution factors and the calculated state density of the rovibrational bath states {|li>} that are permitted by symmetry and angular momentum to couple to the zeroth order optically active rovibrational state |s>. The rotational dependence of the dilution factor shows that the number of mixed states scales linearly with J, where J is the total angular momentum quantum number for the |s> state. Allowing for both Coriolis and Fermi couplings within a width of 0.05 cm-1, we can adequately predict the extent of state mixing and the distribution of the excitation energy among the modes of the molecule by using a straightforward statistical model, which assumes equal coupling between all the zeroth order rovibrational states that have the correct energy, symmetry, and J to couple to a given optically active state. [ABSTRACT FROM AUTHOR]

We have performed an infrared fluorescence study on the intramolecular vibrational relaxation (IVR) from C–H stretch fundamentals in isolated ground state polyatomic molecules. It was found that a density of about 70 combined rotational–vibrational states of a common J and symmetry species per cm-1 is needed to ensure that complex state mixing and IVR occur, although we observed a substantial range of couplings for initial states of the same molecule at higher state densities above the threshold. Propynal was studied as an example of a molecule with a low state density. Fluorescence from propynal shows that although there is substantial state mixing, it is best described as a complicated case of Fermi resonance and Coriolis coupling, as in smaller molecules rather than the multistate mixing seen in larger ones. Infrared fluorescence from terminal C–H stretches of some acetylene derivatives was also measured; these show a slight difference in the extent of IVR from other C–H stretches. Molecules were cooled and isolated in supersonic molecular beams and excited in the C–H stretch region with an optical parametric oscillator. Fluorescence spectra were recorded with either a circular variable filter machine or a cryogenic Michelson interferometer. [ABSTRACT FROM AUTHOR]

The effect of rotational excitation on intramolecular vibrational relaxation in isolated gas phase molecules of dimethyl ether and 1,4 dioxane has been studied. Frequency resolved infrared fluorescence spectra were obtained from molecules isolated in a supersonic expansion and excited in the CH stretching region with an infrared optical parametric oscillator. By altering the expansion conditions the average J of the molecules was controlled. Measurements performed on both molecules at two different rotational temperatures indicate that the dilution factors of the CH stretch modes have a significant J dependence. It is demonstrated that the measured energy contents of the relaxed modes can be satisfactorily modeled by a statistical calculation which assumes equal coupling of all modes with 1 cm-1 of the optical state which conserve J and symmetry. It is shown that the ultimate distribution of the energy within the molecule is J dependent. [ABSTRACT FROM AUTHOR]

Rotationally resolved infrared laser induced fluorescence spectra are presented for dimethyl ether and methyl formate. Q branch spectra are presented for 1,4-dioxane, methyl formate, and dimethyl carbonate. It has been demonstrated earlier that all of these states intramolecularly vibrationally relax. Lower limits on the lifetime of this process are inferred from the present data. For methyl formate and dimethyl ether the J=1 and 2 states have linewidths <0.31 cm-1. This sets a lower limits on the lifetime of 15 ps, although for the limited number of coupled states an exponential decay is not expected. This is also the lower limit for relaxation in the higher J=20 states of 1,4-dioxane and methyl formate, for which exponential decays probably do occur. Dimethyl carbonate relaxes in greater than 10 ps. All measurements were performed in a pulsed supersonic beam with a infrared optical parametric oscillator. [ABSTRACT FROM AUTHOR]