Robert J. Glinski

Effects of isotopic substitution on the chemiluminescence spectra obtained during the reaction of F2 with CS2

Abstract Emission spectra have been obtained during the gas-phase reaction of F2 with CS2 on substitution with carbon-13 and sulfur-34 in effort to ascertain the identity of the emitter. Absence of any measurable shift in the vibronic bands on substitution with carbon-13 suggests that carbon is not present in the emitting molecule and that the previous assignment should be discarded. The measured vibrational frequencies and their shifts on isotopic substitution with sulfur-34 are nearly identical to those that have been reported previously by other workers for the ground electronic state of SF2.

Selenoformaldehyde phosphorescence observed in the reaction of molecular fluorine with dimethyl diselenide.

C(2)-C(8) and C(4)-C(6) distances are extremely close (1.949 (7) and 2.054 (7) A, respectively) as are the corresponding C(2)-C(l)-C(8) and C(4)-C(5)-C(6) bond angles (81.5 (5)O and 88.7 (4)O, respectively). Collectively, the solid-state structure of 1 represents the closest approach to a bishomoaromatic system (1’ in this case) thus far reported. Scrutiny of the nonbonded distances indicates that there are no unusually short contacts involving, e.g., the AlC14gegenion. However, the thermal ellipsoids of C(6) and C(8) are significantly larger than those of the other atoms. The delocalized solid-state structure of 1 stands in sharp contrast to its localized solution-phase structure. Since the bamer to the Cope rearrangement for 1 is similar in magnitude to that of other barbara lane~,~ we are reluctant to invoke any special solvent interactions in the solvation of 1. The structural differences are, therefore, most probably due to crystal packing forces.

Fiberoptic Array Spectroscopy of NH2 in Comet Hale-Bopp: Nature of the Rotational Energy Distributions

Moderate-resolution spectra of the 030 band of NH2 near 6300 A were recorded in Comet Hale-Bopp near 2.6 and 1.0 AU with the HYDRA array spectrometer on the WIYN telescope. The spectra from beyond the collision sphere were examined with respect to the relative rotational energy distributions in NH2. The relative rotational profiles could be consistently fitted at both heliocentric positions by a photostationary state model that follows optical pumping and fluorescence in the 2A1(Πu)- 2B1 band and radiative rotational relaxation in the ground state. The behavior of the spectra with regard to the relative weakness of lines from K = even states at large heliocentric distances is explained by this model, where only the solar flux changes. The general heliocentric dependence of the rotational excitation temperature of collision-free NH2, and, to a first-order approximation, polar diatomic radicals are predicted. The form of the heliocentric dependence is coincidentally similar to that of CO in the collision sphere as observed by others. Species that can undergo optical pumping will show a heliocentric dependence of the rotational excitation temperature of the form Texc(rh) = T1 AU/r. The NH2 radical and diatomic hydrides will have flatter rh dependence than the polar first row diatomics. The rh dependence is largely controlled by the ratio of the fluorescence excitation rate and the rate of radiative rotational relaxation.

Current assessment of the red rectangle band problem

In this paper we discuss our insights into several key problems in the identification of the Red Rectangle Bands (RRBs). We have combined three independent sets of observations in order to try to define the constraints guiding the bands. We provide a summary of the general behavior of the bands and review the evidence for a molecular origin of the bands. The extent, composition, and possible absorption effects of the bands are discussed. Comparison spectra of the strongest band obtained at three different spectral resolutions suggests that an intrinsic line width of individual rotational lines can be deduced. Spectroscopic models of several relatively simple molecules were examined in order to investigate where the current data are weak. Suggestions are made for future studies to enhance our understanding of these enigmatic bands.

Temperature and Velocity Diagnostics of the Red Rectangle from UV Spectra of CO and C I

The UV spectrum of the Red Rectangle and its central source, HD 44179, was examined using the Goddard High Resolution Spectrograph (GHRS) of the Hubble Space Telescope (HST). Spectra have been obtained of the 0-0, 0-1, and 0-2 vibronic bands of the CO fourth positive system, the 1657 A C I multiplet, and the 1931 A C I line. All of the lines and bands display both absorption and emission components. The components do not display P Cygni profiles, but are nearly symmetrically reversed and show different spreads of radial velocity. The widths and Doppler shifts of each component provide information about the environment of its origin, as do the rotational and vibrational distributions in CO. The 1657 A multiplet is too complex for analysis, but the 1931 A line can be deconvolved into two components: emission with narrow velocity dispersion, 25 km s-1, and absorption with a broad velocity dispersion, 230 km s-1. The radial velocity of these atomic features is consistent with the velocity of the center of mass of this known spectroscopic binary. For the CO bands, we obtained a best fit from a four-component model, consistent for all three bands. There are three emission components and one absorption component. Two emission components display narrow velocity spreads (29 km s-1), and one shows a rotational temperature of 50 K, the other, of about 3000 K. The third emission component has a very wide velocity spread (600 km s-1) and a rotational temperature of about 100 K. The absorption component shows a wide velocity spread (230 km s-1) and a rotational temperature of about 100 K. The high-temperature emission displayed partially-resolved rotational line structure corresponding to levels of J = 50. The Doppler shifts of these features place the narrow, cold emission with one of the binary components and the narrow, hot emission with the center of mass. We discuss these observations with respect to the accretion disk model of this object. We also compare our UV CO observations with the work of others on the IR CO overtone spectra in young stellar objects.

Observation of the Spin-Forbidden Cameron Bands of CO in the Ultraviolet Emission Spectrum of the Red Rectangle

The center of the biconical nebula known as the Red Rectangle has been observed by using the ultraviolet spectrographs aboard the Hubble Space Telescope. We report the observation of phosphorescence of the Cameron bands of CO (a3Π → X1Σ+) between 1850 and 2600 A. These bands are seen for the first time outside of the solar system. The bands are about one-fifth as strong as the accompanying emission bands of the spin-allowed Fourth Positive system. A charged-particle impact excitation mechanism is suggested for the direct production of CO (a3Π) from CO (X1Σ+). The C I (1D-1Po) line is observed at 1931 A, suggesting that a large amount of C I (1D) is also present.

Chemiluminescence from Sulfur Compounds in Novel Flame and Discharge Systems: Proof of Sulfur Dioxide as the Emitter in the New Sulfur Chemiluminescence Detector

Gases from a hydrogen-rich, sulfur-dioxide-containing, hydrogen/oxygen flame were drawn into a reduced-pressure reaction vessel and reacted with ozone. Spectroscopic analysis of the low-pressure chemiluminescence showed that electronically excited sulfur dioxide is the principal emitter exploited in the new sulfur chemiluminescence detector (SCD). Sulfur dioxide phosphorescence was found to contribute significantly to the total emission, suggesting that the technique could be enhanced by detecting more of the phosphorescence at higher total pressures. A calibration plot of signal vs. sulfur dioxide concentration was found to have a slight positive curvature. Interferences from NO2* and OH* were spectroscopically characterized; it is suggested that these could be minimized in the SCD by judicious choice of the wavelength discrimination filter. Utilization of a microwave discharge was similarly efficient at producing the chemiluminescence.

Oxygen/hydrogen chemistry in the inner comae of active comets

We have constructed a concentric-shell, one-dimensional kinetic model that examines the chemistry of hydrogen and oxygen species in detail. We have studied the effects of the reactions of the reactive OH, O( 3 P), and O( 1 D) species with themselves and with the abundant stable molecules in the inner coma of moderately and highly active comets. We find that the reactions (1) Oð 1 DÞþH2O! 2OH and (2) Oð 3 PÞþOH! O2þ Hp lay important roles in the inner comae of active comets. Inclusion of reaction (2) predicts the formation of significant amounts of molecular oxygen. As the densities of O2 may be as high as 1% those of water in some cases, the possibility of detection exists. We suggest the possibility that the ion O þ may contribute to some previously unassigned features in the optical ion-tail spectra of comets. We also consider the role that reactions of the reactive species might play in the destruction of CO, NH3, and organic molecules in the inner coma of the active comet. We find that destruction offormaldehyde, for example, by reaction with OH has a small but essentially negligible effect on the predicted production rate offormaldehyde. Finally, we examine the significance of the reaction of OH with CO in the dense inner coma. Subject headings: astrochemistry — comets: general

Examination of sulfur forms in coal by direct pyrolysis and chemiluminescence detection

Abstract The extremely high selectivity of the newly developed ozone-sulfur chemiluminescence detector (SCD) coupled with controlled-temperature pyrolysis, was applied to the qualitative and semiquantitative determination of sulfur forms in coal. Pyrolysis products from the heating of a sulfur-containing solid sample were swept directly through a high-temperature conversion tube and into the SCD to yield a strong signal. Upon heating the pyrolysis tube from room temperature to 700°C, several distinct peaks were observed by the SCD, identified as being due to aliphatic sulfides and thiols, elemental sulfur, simple thiophenes, pyrite and complex thiophenes. Standard additions of pure inorganic substances provided semiquantitative determination. Three coals were examined and could be quickly and easily distinguished by their sulfur forms. The results are compared with those of other pyrolysis methods.

Can the Red Rectangle Molecular Emission Bands Be Assigned to C

We review the current information on the unique group of visibleemission bands known as the Red Rectangle bands (RRBs). A laboratoryspectrum exactly matching these bands is not yet available; however, thereis sufficient reason to hypothesize phosphorescence from C3 asthe source. The points in favor of the C3/RRB hypothesis canbe summarized as follows: (1) The RRBs are found in the spatial locationwhere carbonaceous grains are being impinged upon by a bipolar outflow. (2)C3 is known to accompany circumstellar carbon grains and mayconstitute a ‘magic’ fragment in the UV photofragmentation ofCn clusters. (3) Our recent observation of the spin-forbiddenCO Cameron emission bands in this object suggests that charged particleimpact excites triplet states. (4) The energy of the lowest triplet state ofC3 is known to be very close to that of the RRBs. (5) The RRBsdisplay a vibrational spacing that is quantitatively consistent withC3, including a rare negative anharmonicity.