Absolute absorption cross sections at high resolution in the A2Πi – X2Πi band system of ClO

1984 ◽  
Vol 62 (5) ◽  
pp. 473-486 ◽  
Author(s):  
S. A. Barton ◽  
J. A. Coxon ◽  
U. K. Roychowdhury
Keyword(s):  
Cross Sections ◽  
Column Density ◽  
Flow System ◽  
Band System ◽  
Nonlinear Least Squares ◽  
Synthetic Spectrum ◽  
Electronic Transition Moment ◽  
Chlorine Monoxide ◽  
Fast Flow ◽  
Least Squares Techniques

Chlorine monoxide (ClO) has been produced at temperatures near 315 K in a fast-flow system at total pressures (of argon diluent) in the range 1.0–2.0 mm Hg. The transmittance of ultraviolet radiation has been determined with a spectral resolution of 0.0054 nm for all 35ClO ν′–0 A2Π3/2 – X2Π3/2 sub-bands in the range 3 ≤ ν′ ≤ 12 (305.9–274.9 nm). The ClO column density obtained with 8 or 12 traversals of the radiation along an 80 cm cell was in the range 1.0–2.0 × 1017 cm−2.The experimental transmittance profiles for each sub-band have been reproduced closely by synthetic spectrum calculations. The parameters required as input to the programs were optimized by nonlinear least-squares techniques. The fitted (Lorentzian) linewidths are on average more than double those previously reported from visual estimates of linewidths on photographic plates. The fitted band strengths lead to a well-defined electronic transition moment variation for the A – X system of ClO, which is in excellent agreement with an earlier determination by Mandelman and Nicholls from spectra at lower resolution (0.22 nm) with unresolved rotational structure.

A Spectrometric Technique for Monitoring [O2(a1 Δg)] in the Gas Phase

1986 ◽  
Vol 40 (2) ◽  
pp. 203-209 ◽  
Author(s):  
J. A. Coxon ◽  
U. K. Roychowdhury
Keyword(s):  
Gas Phase ◽  
Cross Sections ◽  
Flow System ◽  
Germanium Detector ◽  
Hydrogen Emission ◽  
Partial Pressures ◽  
Hydrogen Emission Lines ◽  
Fast Flow ◽  
Vacuum Uv ◽  
Absorption Of Hydrogen

The reaction of chlorine with alkaline hydrogen peroxide has been used to produce O2( a1 Δ g) in a fast flow system at partial pressures up to about 0.5 Torr, and total pressures (mostly argon) in the range 0.8–2.5 Torr. Absolute concentrations of O2( a1 Δ g) were determined from the intensity of absorption of hydrogen emission lines in the vacuum-UV at 144.095 and 148.66 nm, for which the cross sections are known. The intensity of the O2 ( a → X) transition at 1270 nm, monitored simultaneously with a simple germanium detector, was found to vary linearly with [O2( a1 Δ g)], as expected. The germanium detector was calibrated at 1270 nm with a readily reproducible standard, the air afterglow continuum due to NO2* at defined concentrations of O(3P) and NO. The ratio of ka for O2( a) ka O 2( X) + hvt to kc for O + NO kc NO2 + hv, is (1.4 ± 0.2) × 10−7 mol L−1 at 1270 nm.

scholarly journals Photoproduction of H3+ from gaseous methanol inside dense molecular clouds

2008 ◽  
Vol 4 (S251) ◽  
pp. 369-370
Author(s):  
S. Pilling ◽  
D. P. P. Andrade ◽  
A. C. F. Santos ◽  
H. M. Boechat-Roberty
Keyword(s):  
Cross Sections ◽  
Molecular Clouds ◽  
Mass Spectra ◽  
Column Density ◽  
X Rays ◽  
Alternative Source ◽  
X Ray ◽  
Flight Mass Spectrometry ◽  
Dense Molecular Cloud ◽  
Synchrotron Light

AbstractWe present experimental results obtained from photoionization and photodissociation processes of abundant interstellar methanol (CH3OH) as an alternative route for the production of H3+ in dense clouds. The measurements were taken at the Brazilian Synchrotron Light Laboratory (LNLS) employing soft X-ray and time-of-flight mass spectrometry. Mass spectra were obtained using the photoelectron-photoion coincidence techniques. Absolute averaged cross sections for the production of H3+ due to molecular dissociation of methanol by soft X-rays (C1s edge) were determined. The H3+'s photoproduction rate and column density were been estimated adopting a typical soft X-ray luminosity inside dense molecular and the observed column density of methanol. Assuming a steady state scenario, the highest column density value for the photoproduced H3+ was about 1011 cm2, which gives the ratio photoproduced/observed of about 0.05%, as in the case of dense molecular cloud AFGL 2591. Despite the small value, this represent a new and alternative source of H3+ into dense molecular clouds and it is not been considered as yet in interstellar chemistry models.

scholarly journals The Mass Spectrum of Interstellar Clouds

1989 ◽  
Vol 120 ◽  
pp. 511-517
Author(s):  
John M. Dickey ◽  
R. W. Garwood
Keyword(s):  
Cross Sections ◽  
Molecular Clouds ◽  
Column Density ◽  
Unit Volume ◽  
Empirical Relationship ◽  
Line Of Sight ◽  
Interstellar Clouds ◽  
Absorption Studies ◽  
Low Latitudes ◽  
Diffuse Clouds

AbstractThe abundance of 21-cm absorption lines seen in surveys at high latitudes can be translated into a line of sight abundance of clouds vs. column density using an empirical relationship between temperature and optical depth. As VLA surveys of 21-cm absorption at low latitudes are now becoming available, it is possible to study the variation of this function with galactic radius. It is interesting to compare the abundance of these diffuse atomic clouds (with temperatures of 50 to 100 K and masses of 1 to 10 M⊙) to the abundance of molecular clouds. To do the latter we must make assumptions about cloud cross-sections in order to convert the line of sight abundance of diffuse clouds into a number per unit volume, and to convert from cloud column density to mass. The spectrum of diffuse clouds matches fairly well the spectrum of molecular clouds, although observationally there is a gap of several orders of magnitude in cloud mass. Optical absorption studies also agree well with the 21-cm results for clouds of column density a few times 1020 M⊙.

scholarly journals Re-exploring Molecular Complexity with ALMA (ReMoCA): interstellar detection of urea

2019 ◽  
Vol 628 ◽  
pp. A10 ◽  
Author(s):  
A. Belloche ◽  
R. T. Garrod ◽  
H. S. P. Müller ◽  
K. M. Menten ◽  
I. Medvedev ◽  
...  
Keyword(s):  
Column Density ◽  
High Mass ◽  
Synthetic Spectrum ◽  
Mass Star ◽  
Methyl Isocyanate ◽  
Vibrationally Excited ◽  
Data Set ◽  
Star Forming ◽  
Order Of Magnitude ◽  
Molecular Complexity

Context. Urea, NH2C(O)NH2, is a molecule of great importance in organic chemistry and biology. Two searches for urea in the interstellar medium have been reported in the past, but neither were conclusive. Aims. We want to take advantage of the increased sensitivity and angular resolution provided by the Atacama Large Millimeter/submillimeter Array (ALMA) to search for urea toward the hot molecular cores embedded in the high-mass-star-forming region Sgr B2(N). Methods. We used the new spectral line survey named ReMoCA (Re-exploring Molecular Complexity with ALMA) that was performed toward Sgr B2(N) with ALMA in its observing cycle 4 between 84 and 114 GHz. The spectra were analyzed under the local thermodynamic equilibrium approximation. We constructed a full synthetic spectrum that includes all the molecules identified so far. We used new spectroscopic predictions for urea in its vibrational ground state and first vibrationally excited state to search for this complex organic molecule in the ReMoCA data set. We employed the gas-grain chemical kinetics model MAGICKAL to interpret the astronomical observations. Results. We report the secure detection of urea toward the hot core Sgr B2(N1) at a position called N1S slightly offset from the continuum peak, which avoids obscuration by the dust. The identification of urea relies on nine clearly detected transitions. We derive a column density of 2.7 × 1016 cm−2 for urea, two orders of magnitude lower than the column density of formamide, and one order of magnitude below that of methyl isocyanate, acetamide, and N-methylformamide. The latter molecule is reliably identified toward N1S with 60 clearly detected lines, confirming an earlier claim of its tentative interstellar detection. We report the first interstellar detections of NH2CH18O and 15NH2CHO. We also report the nondetection of urea toward the secondary hot core Sgr B2(N2) with an abundance relative to the other four species at least one order of magnitude lower than toward the main hot core. Our chemical model roughly reproduces the relative abundances of formamide, methyl isocyanate, acetamide, and N-methylformamide, but it overproduces urea by at least one order of magnitude. Conclusions. Urea is clearly detected in one of the hot cores. Comparing the full chemical composition of Sgr B2(N1S) and Sgr B2(N2) may help understand why urea is at least one order of magnitude less abundant in the latter source.

HgCl B2Σ+1/2 formation by low-energy electron impact dissociation of HgCl2 and(or) CH3HgCl molecules: applications to HgCl (B → X) laser

1990 ◽  
Vol 68 (2) ◽  
pp. 166-169 ◽  
Author(s):  
Mohammad F. Mahmood
Keyword(s):  
Energy Range ◽  
Electron Energy ◽  
Cross Sections ◽  
Band System ◽  
Low Energy ◽  
Dissociative Excitation ◽  
Intense Band ◽  
Electron Impact Dissociation ◽  
Low Energy Electrons ◽  
Low Energy Electron

An investigation was made of the process of dissociative excitation of a HgCl radical in the B2Σ+1/2 state due to collisions of low-energy electrons with HgCl2 and CH3HgCl molecules. Using the most intense band of the B2Σ+1/2 – X2Σ+1/2 system of the HgCl radical at 557 nm that corresponds to the ν′ = 0 to ν″ = 22 transition, emission cross sections were measured in the electron energy range 1–100 eV. The threshold electron energy for the observation of the B2Σ+1/2 – X2Σ+1/2 band system has been determined to be 7.0 and 8.0 eV for HgCl2 and CH3HgCl molecules, respectively.

The Rate of Recombination of H Atoms in the Presence of NH3

1973 ◽  
Vol 51 (22) ◽  
pp. 3771-3773 ◽  
Author(s):  
L. Teng ◽  
C. A. Winkler
Keyword(s):  
Rate Constant ◽  
Pressure Range ◽  
Flow System ◽  
Carrier Gas ◽  
A Value ◽  
Fast Flow

The rate constant for the homogeneous recombination of H atoms in the presence of NH3, with He as carrier gas, has been determined at 298°K in a fast flow system, over the pressure range 1.50 to 4.55 Torr, using e.s.r. technique. A value of either 4.00 × 1016 or 5.14 × 1016 cm6 mol−2 s−1 was calculated, depending upon the rate constant taken, or estimated, from the literature for the recombination in the presence of helium.

Sign in / Sign up

Export Citation Format

Share Document