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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.

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

We have observed the Red Rectangle nebula with the Multi-Object Spectrograph on the WIYN telescope. Moderate-resolution spectra (Δλ=0.4 A) in the region of 5800 A were obtained in 3-arcsec apertures at over 50 positions in the nebula. Accurate and precise wavelength calibrations were obtained against a thorium–argon lamp and the sodium lines in the sky and nebula. The peak position and full width at half-maximum of the 5800-A Red Rectangle band (RRB) were measured to beyond 15 arcsec from the star. The shortest wavelength of the band is found to be 5799.10±0.15 A in the rest frame of the nebula. None of the emission bands has intensity coincident with the wavelength of the diffuse interstellar band (DIB) at 5797.11±0.05 A. The 2-A offset cannot be explained by an instrumental, spectroscopic or photophysical effect. The hypothesis that the same molecule may be the carrier of the RRB and the DIB is contradicted by these observations. As a further test of the hypothesis, absorption has been sought that would be due to a potential DIB carrier in the nebula. Tentative evidence for absorption is found in the RRB spectra taken within 9 arcsec of the star; but any absorption has a peak position essentially coincident in wavelength with the band maximum of the emission band.

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.

We have calculated synthetic spectra of perpendicular and parallel rovibronic bands of cumulene carbene molecules of the form CnH2. The perpendicular bands are consistent with a regularly spaced group of diffuse interstellar bands (DIBs) near 6850 A. Parallel bands calculated for these molecular structures are consistent with the intrinsic profile of the associated 6614-A DIB. Both types of bands are expected for an electronic transition that these species should have at those energies. We could not determine if the molecule was charged or if an atom other than carbon terminated the chain-end. Constraints due to molecular geometry and temperature place the chain length at 7–15 carbons to fit the 6850-A group and 9–13 carbons to fit the 6614-A DIB.

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.

We investigate the fates and population densities of the vibrationally excited homonuclear diatomic molecules HzIH;, CJC2+ and OJO; in interstellar conditions using photochemical kinetic models. We find that the population distribution of vibrationally excited H2 + resembles the nascent distribution from the cosmic ray ionization of H2 under several cloud conditions. We predict that the density of H; (v) could exceed that of H2(v) under certain cloud conditions. Based on this we present a synthetic spectrum of the quadrupole-allowed infrared emission from H; (v). Our results for Hz(v) are in accord with those of previous workers. The vibrationally excited states of C2 and O2 show abundances on the order of 10 - 4 ofthe ground state. We emphasize that these populations are controlled by reaction dynamics and photochemical kinetics, and do not resemble those of the local thermodynamic equilibrium (LTE). Preliminary models of the Cz+(v) and O;(v) chemistry show that the vibrational distributions will somewhat resemble the nascent distributions of the reactions which create them. Further experimental or theoretical studies of the dynamics of these reactions are necessary before quantitative predictions can be made.

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.

A basic model for the formation of non-equilibrium rotational energy distributions is described for reactive, homo-polar diatomic molecules and ions in the interstellar medium. Kinetic models were constructed to calculate the rotational populations of $\mathrm{C}_{2}^{+}$ under the conditions it would experience in the diffuse interstellar medium. As the non-polar ion reacts with molecular hydrogen, but not atomic hydrogen, the thermalization of a hot nascent rotational population will be arrested by chemical reaction when the H2 density begins to be significant. Populations that deviate strongly from the local thermodynamic equilibrium are predicted for $\mathrm{C}_{2}^{+}$ in environments where it may be detectable. Consequences of this are discussed and a new optical spectrum is calculated.

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.

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.

Moderate-resolution chemiluminescence spectra of CD{sub 2}S, CH{sub 2}S, and CH{sub 2}Se were obtained during the reaction of F{sub 2} with methylated sulfur and selenium compounds at about 0.5 Torr of total pressure. Phosphorescence corresponding to the {tilde a}{sup 3}A{sub 2} {yields} {tilde X}{sup 1}A{sub 1} transition dominated all the spectra, and a trace of fluorescence, {tilde A}{sup 1}A{sub 2} {yields} {tilde X}{sup 1}A{sub 1}, appeared only in the spectrum of CH{sub 2}Se. The v{sub 4} and v{sub 6} frequencies of the {tilde a} state of CD{sub 2}S are reported for the first time as 219.4 {plus minus} 5.0 and 572.6 {plus minus} 5.0 cm{sup {minus}1}, respectively. From the unusually shaped 4{sub 1}{sup 1} band of CH{sub 2}S ({tilde a} {yields} {tilde X}) an improved value of the v{prime}{sub 4} frequency was found to be 308 {plus minus} 30 cm{sup {minus}1}. The CH{sub 2}Se yielded an improved measurement of the v{double prime}{sub 3} frequency, 860 {plus minus} 10 cm{sup {minus}1}, and new estimates of three other ground-state frequencies: v{double prime} = 1,460 {plus minus} 30, v{double prime}{sub 4} = 906 {plus minus} 10, and v{double prime} = 914 {plus minus} 10, and v{double prime}{sub 6} = 914 {plus minus} 20 cm{supmore » {minus}1}. A spectrum of CH{sub 2}Te was sought in the reactions of CH{sub 3}TeCH{sub 3} and CH{sub 3}Te{sub 2}CH{sub 3} with F{sub 2} but was not found; instead emission from TeF (A{sup 2}{pi}{sub i} {yields} X{sup 2}{pi}{sub 1}) was observed.« less

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.

Moderate-resolution chemiluminescence spectra of CD{sub 2}S, CH{sub 2}S, and CH{sub 2}Se were obtained during the reaction of F{sub 2} with methylated sulfur and selenium compounds at about 0.5 Torr of total pressure. Phosphorescence corresponding to the {tilde a}{sup 3}A{sub 2} {yields} {tilde X}{sup 1}A{sub 1} transition dominated all the spectra, and a trace of fluorescence, {tilde A}{sup 1}A{sub 2} {yields} {tilde X}{sup 1}A{sub 1}, appeared only in the spectrum of CH{sub 2}Se. The v{sub 4} and v{sub 6} frequencies of the {tilde a} state of CD{sub 2}S are reported for the first time as 219.4 {plus minus} 5.0 and 572.6 {plus minus} 5.0 cm{sup {minus}1}, respectively. From the unusually shaped 4{sub 1}{sup 1} band of CH{sub 2}S ({tilde a} {yields} {tilde X}) an improved value of the v{prime}{sub 4} frequency was found to be 308 {plus minus} 30 cm{sup {minus}1}. The CH{sub 2}Se yielded an improved measurement of the v{double prime}{sub 3} frequency, 860 {plus minus} 10 cm{sup {minus}1}, and new estimates of three other ground-state frequencies: v{double prime} = 1,460 {plus minus} 30, v{double prime}{sub 4} = 906 {plus minus} 10, and v{double prime} = 914 {plus minus} 10, and v{double prime}{sub 6} = 914 {plus minus} 20 cm{supmore » {minus}1}. A spectrum of CH{sub 2}Te was sought in the reactions of CH{sub 3}TeCH{sub 3} and CH{sub 3}Te{sub 2}CH{sub 3} with F{sub 2} but was not found; instead emission from TeF (A{sup 2}{pi}{sub i} {yields} X{sup 2}{pi}{sub 1}) was observed.« less

Phosphine, alkylated phosphines and monophosphinate esters are detected with high sensitivity in capillary gas chromatography (GC) by their chemiluminescent reactions with molecular fluorine. Detection limits are estimated to be 1.3 pg, 0.5 pg, 8 pg, and 17 pg for phosphine, trimethyl phosphine, trimethyl phosphinate ester, and triethyl phosphine, respectively. As found earlier with alkylated sulfur, selenium and tellurium compounds, the detector exhibits a linear response. For triethyl phosphine, a linear range of greater than three orders of magnitude was demonstrated. Emission spectra were obtained for the trimethyl phosphine and triethyl phosphine systems. Chemiluminescence emitters include electronically excited HCF, vibrationally excited HF, and an unknown species in the trimethyl phosphine system. Banded emission from vibrationally excited HF and a broad continuum were observed for both trimethyl phosphine and triethyl phosphine; however, HCF emission was observed only for TMP. Under the conditions employed, the principal emitter is HCF for trimethyl phosphine and HF and the unknown emitter for triethyl phosphine. This detector may have important applications in investigations of the biogeochemical cycling of phosphorus.

We have re-analyzed the ultraviolet spectrum of HD 44179, the central star(s) of the Red Rectangle nebula, providing improved estimates of the column density, rotational, and vibrational temperatures of the 4th Positive A-X system of CO in absorption. The flux shortward of 2200 A is a complex blend of CO features with no discernible stellar photosphere, making the identification of other molecular species difficult, and the direct derivation of the dust extinction curve impossible. We confirm that the spin-forbidden CO (a-X) Cameron bands are likely produced by either collisional excitation or a chemical reaction, not photoexcitation, but with a higher internal vibrational excitation than previously determined. We also detect the spin-forbidden CO a'-X, d-X, and e-X absorption features. The hot CO (A-X) bands exhibit a blue-shift of ~300 km/s, likely occurring close to the white dwarf star(s) suspected as the original source of the ultraviolet flux in the system, and forming the base of the outflow of material in the Red Rectangle. The OH "comet-band" system near 3000 A is also analyzed, and estimates of its rovibrational temperatures determined. The source of the molecules studied in this system is still unknown, but may be a combination of gaseous material associated with the star(s), or processed material from the surrounding dust torus., Comment: 40 pages, 14 figures

An electronic emission spectrum of SF{sub 2} extending from 5,500 to 8,500 {angstrom} is observed during the reactions of F{sub 2} with CS{sub 2}, OCS, and sulfur vapor. Long vibrational band progressions of 355 {plus minus} 2 cm{sup {minus}1} and short progressions of 838 {plus minus} 2 cm{sup {minus}1} are definitively assigned to v{sub 2}{double prime} and v{sub 1}{double prime}, respectively. Isotopic substitution of CS{sub 2} with sulfur-34 has allowed a tentative assignment of the third ground-state frequency, v{sub 3}{double prime} = 817 {plus minus} 6 cm{sup {minus}1}, and the electronic origin, 18,123 {plus minus} 1,000 cm{sup {minus}1}. Ground-state frequencies and their isotopic shifts compared very well with those obtained in infrared absorption experiments by other workers. Estimates of the anharmonicities of the ground-state frequencies are presented. Results of first principles electronic energy calculations are presented, showing that two low-lying singlet electronic states are in the energy range of this emission spectrum. A discussion is presented relating the possible activity of the asymmetric stretch and the nature of the excited electronic state.

A survey is presented of possible binary azeotropic systems suitable for study in an undergraduate physical chemistry laboratory. From a range of sources, a list has been compiled of the most acceptable systems on the basis of health, safety, waste disposal, and practicability concerns. More than 80 systems were reviewed.

Only recently have groups of diffuse interstellar bands (DIBs) been observed to have regular structure lending new hope for the identification of the bands' origins. Herbig has reported a group of bands between 6770 and 6860 A which seem to show regular spacing and intensity alternation. We suggest that these bands resemble perpendicular vibronic bands in a molecule of the form CH2X. As the Herbig group lies very near an expected transition of similar form in thioformaldehyde, CH2S, an analysis of the absorption spectrum of that molecule was made to determine if it had other bands in common with the DIB spectrum. Six prominent, red-shaded, sharp, single-headed bands were calculated, based on laboratory data, to have absolute frequency positions within 2 cm-1 of those for the corresponding DIBs. The transitions would originate from the 2y3 level in the ground electronic state of thioformaldehyde, suggesting that vibrationally hot bands in the transition A1A2

The spectra from the chemiluminescent reactions of ozone with dimethyl sulfoxide and dimethyl disulfide ((CH/sub 3/S)/sub 2/) have been studied at low pressure in a beam-gas apparatus. The chemiluminescence emission for each reaction was monitored as a function of the ozone and fuel pressures over a total pressure range from 0.05 to 50 mtorr. In the reaction of ozone with dimethyl sulfoxide weak, unstructured emission was observed in the region from 280 to 500 nm. This emission was found to be congruent to that observed in the reactions of ozone with H/sub 2/S, CH/sub 3/SH, and CH/sub 3/SCH/sub 3/ under similar conditions and was attributed to fluorescence from electronically excited SO/sub 2/. The reaction of ozone with (CH/sub 3/S)/sub 2/ also yielded broad-band fluorescence from SO/sub 2/ as well as a vibrationally resolved SO/sub 2/ phosphorescence feature. Chemiluminescence from the HSO radical was observed to the red of 530 nm in the reaction of ozone with (CH/sub 3/S)/sub 2/. Mechanisms have been proposed for each reaction based on the character of the luminescence and the dependence of the emission on reactant pressure. Results are contrasted with previous work on other simple sulfides. 25 references, 8 figures.

Chimiluminescence visible. Une partie de cette emission correspond a OH * (A 2 Σ + →X 2 π i ) a 310 nm. Une espece importante emettrice semble etre H 2 SiO 2

Rich chemiluminescence is observed in the gas phase reactions of F2 with a variety of organosulfur compounds at room temperature and from 0.2 to 2.0 Torr. HCF(A1A″) and vibrationally excited HF are observed in the reaction of F2 with all the hydrogen-bearing compounds under varying conditions of reactant pressure. For the organosulfur reactants used in this study, CH2S(a 3A2) is observed only with CH3SH, CH3SCH3 and CH3SSCH3. The character of the emission spectra changes dramatically with changing reactant pressures or when CH3OH or CH3CH are present. CH2S* is observed with CH3CH2SH and higher thiols when CH3OH is present. A new vibrationally structured spectral feature appears ubiquitously in all of the reaction systems studied, and distinctly in the reaction of F2 with CS2. It is ascribed to an electronic transition of the transient species, FCS. The initiation of the reactions of F2 with the stable organosulfur species and the implications of this work for IR multiphoton dissociation are discussed.

We have observed phosphorescence from the a 3 A 2 state of CH 2 S and CD 2 S produced in the gas-phase chemiluminescent reactions of F 2 with CH 3 SH and CD 3 SH. We have measured the υ 4 ′ = 1 frequency of the a 3 A 2 state for both molecules. Vibrationally excited HF emission was superimposed on both spectra but no DF emission was observed.

Attribution des bandes vibrationnellement resolues a SeF(A−X), Se 2 (A−X) et Se 2 (B−X). Observation d'un nouveau systeme de bandes vibroniques non resolues. Comparaison avec les resultats de la reaction de F 2 avec CS 2

The spectra from the chemiluminescent reactions of ozone with dimethyl sulfoxide and dimethyl disulfide ((CH/sub 3/S)/sub 2/) have been studied at low pressure in a beam-gas apparatus. The chemiluminescence emission for each reaction was monitored as a function of the ozone and fuel pressures over a total pressure range from 0.05 to 50 mtorr. In the reaction of ozone with dimethyl sulfoxide weak, unstructured emission was observed in the region from 280 to 500 nm. This emission was found to be congruent to that observed in the reactions of ozone with H/sub 2/S, CH/sub 3/SH, and CH/sub 3/SCH/sub 3/ under similar conditions and was attributed to fluorescence from electronically excited SO/sub 2/. The reaction of ozone with (CH/sub 3/S)/sub 2/ also yielded broad-band fluorescence from SO/sub 2/ as well as a vibrationally resolved SO/sub 2/ phosphorescence feature. Chemiluminescence from the HSO radical was observed to the red of 530 nm in the reaction of ozone with (CH/sub 3/S)/sub 2/. Mechanisms have been proposed for each reaction based on the character of the luminescence and the dependence of the emission on reactant pressure. Results are contrasted with previous work on other simple sulfides. 25 references, 8 figures.

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.