Ion-molecule Reaction Scheme Research Articles

Pressure-dependent mobility of negative ions in mixtures of H2O with Ar

The mobility of negative ions in H2O–Ar mixtures has been measured with a pulsed Townsend technique. It has been found that for a fixed value of the density-normalized electric field strength, E/N, the mobility of the H2O anions is strongly pressure dependent. We have also found that even for a single, total gas mixture pressure, even though at first sight the mobility of the anions seems to follow Blanc’s relation closely, a closer view indicates that the mobilities tend to shift to higher values as the water vapour concentration decreases. In spite of the lack of mass spectrometry to assess the mass and abundance of the drifting anions under specific conditions of E/N, water vapour concentration and gas pressure, the present measurements are strongly indicative of a complex ion transport and ion-molecule reaction scheme of daughter H2O anions in the H2O–Ar mixture.

Drift and clustering of daughter negative ions of H2O in parent gas

The mobility of daughter negative ions of H2O in parent gas has been measured with a pulsed Townsend technique over the density-reduced field strength, E/N, range 9–100 Td and a pressure range 2–16 Torr. It has been found that the mobility of the anions is dependent on the gas pressure. Using a transport theory considering the influence of the permanent dipole field of H2O, we have found that the pressure-dependent mobilities can be associated with a series of cluster ions of the type OH−(H2O)n (n = 1–3), with the mass of the cluster species increasing with the total gas pressure. Also, the mobility of H− and OH− could be estimated. Using a Townsend avalanche simulator we have been able to explain the measured ionic currents in terms of an ion–molecule reaction scheme with a single set of swarm and reaction coefficients for each value of the density-reduced field strength, E/N, at several pressures. Regarding the positive ions, the only drifting ion is H3O+, the mobility of which could be estimated. The rate constants relative to the formation of the OH−(H2O)n (n = 1–3) species were also derived from this study.

Stratospheric chemical ionization mass spectrometry: nitric acid detection by different ion molecule reaction schemes

Detailed height profiles of stratospheric nitric acid mixing ratios have been derived with a baloon borne chemical ionization mass spectrometer by applying several ion molecule reaction schemes, each associated to a specific and selective ion source. These ions (CO 3 −, Cl n −, CF 3O −, and CF 3O −H 2O) give rise to specific product ions (mainly CO 3 −HNO 3, NO 3 −HCl, NO 3 −HF, and CF 3O −HNO 3) upon reaction with ambient nitric acid molecules. This paper reports on the instrumental details as well as on the results obtained during two balloon flights with the instrument. Within the accuracy of the measurements, the nitric acid height profiles obtained with the three different ion sources are in good agreement with one another as well as with literature data.

Infrared spectroscopy of carbo-ions. III. ν3 band of methyl cation CH+3

The infrared spectrum of the degenerate ν3 vibration–rotation band of methyl cation CH+3, one of the most fundamental carbo-ions, has been observed and analyzed. The spectrum was observed in the frequency range of 3240–2960 cm−1 using the difference frequency laser system as the tunable coherent infrared source. A gas mixture of He:H2:CH4∼700:20:1 with a total pressure of ∼7 Torr was used for the ac discharge in an air-cooled and a water-cooled multiple inlet–outlet discharge tube. The velocity modulation method together with noise subtraction and the unidirectional multiple passing of the beam was used for high sensitivity. The spectral lines of CH+3 appeared amid many other lines of C2H+2 and C2H+3 but their widths and their response to chemical conditions gave a good initial clue for the identification. Over 200 absorption lines have been assigned to CH+3 and the isotopic species 13CH+3. The spectral pattern clearly shows that the equilibrium molecular structure is a planar, equilateral triangle as expected from Herzberg’s Rydberg spectrum of CH3 and from ab initio theory. The spectrum has been analyzed by using the symmetric rotor Hamiltonian in a degenerate vibrational state with various A1–A2 splittings and l resonance. The spectral lines have been least-squares fit with a standard deviation of 0.0058 cm−1, and led to 21 vibration–rotation constants of CH+3. Several analytical expressions have been derived among these constants to determine the structure and potential constants. Some perturbation has been noticed and discussed. Also quite a few lines which are definitely due to carbocations with one carbon atom have been left unassigned. The prominence of the CH+3 spectrum in hydrocarbon discharges confirms the importance of this species in the ion–molecule reaction scheme in the laboratory and in space which has already been noted by many people in the field. A simple discussion is given about the formation and destruction of CH+3 as well as other carbocations.

Tricarbon monoxide in TMC-1.

We report the measurement of three new lines of C3O in TMC-1. The observed peak antenna temperatures, appropriately corrected for atmospheric and telescope losses, are found to be consistent with a large velocity gradient radiative transfer model whose parameters span the range of standard values for this cloud. The derived fractional abundance for C3O is 1.4 x 10(-10), comparable with the results predicted from a model calculation based on a gas-phase ion-molecule reaction scheme. The results of negative searches for C3O in six other sources are not inconsistent with expected conditions in these clouds.

Interstellar H3(+) - Possible detection of the 1(10)-1(11) transition of H2D

An interstellar line has been detected in emission at the expected submillimeter wavelength of the 1(10)-1(11) transition of H2D(+), the deuterated verison of the primary ion (H3/+/) in the favored ion-molecule reaction scheme for interstellar gas phase chemistry. The strength of the line is in approximate agreement with the theoretically anticipated H2D(+) abundance.

Millimeter- And Submillimeter-Wave Receivers

This review is concerned with recent developments in the design and implementation of radio-type heterodyne mixer receivers for millimeter- and submillimeter-wave astronomy. For the most part these receivers will be used for spectroscopy of the interstellar medium. Understanding of the nature of the interstellar medium has increased enormously in the last decade, in large part due to studies of interstellar molecule rotation transitions (Rank et al. 1971, Zuckerman & Palmer 1974, Thaddeus 1977). Line emission or absorption can be seen due to molecular clouds with hydrogen molecule densities ranging from 10^3-10^8 cm^(-3). This has led to improved understanding of galactic structure (Cohen et al. 1980), star formation (Elmegreen & Lada 1977), and stellar mass loss processes (Zuckerman 1980). Studies of molecule emission in external galaxies are also developing (Rickard et al. 1977). From a chemical viewpoint there has been a similar surge forward in understanding, with the identification of interstellar species such as HCO^+ (Hollis et al. 1975, Woods et al. 1975, Snyder et al . 1976) which occur in the theoretical ion-molecule reaction schemes (Herbst & Klemperer 1973, Watson 1975).

HCO/+/ emission in the galacic center region. I - Observations

HCO/sup +/ emission (3.4 mm, J=1--0) in the galactic center region has been observed toward the dense molecular clouds near Sgr A and Sgr B2 at over 20 points. The profiles are asymmetric, and are very widely extended in velocity like the /sup 12/CO line in spite of the high excitation requirements of the HCO/sup +/ line. A position-velocity map along the galacitc plane including the galactic nucleus was obtained. Comparison with the HCN emission leads us to the conclusion that the number density ratio (HCO/sup +/)/(HCN) is higher by an order of magnitude in the diffuse region. This behavior is discussed in terms of the ion-molecule reaction scheme. A dip of 0 km s/sup -1/, which is probably due to self-absorption by foreground cold molecular gas, was found in the HCO/sup +/ profiles as well as in spectra of HCN. The abundance of HCO/sup +/ relative to H/sub 2/ in the cold cloud is estimated to be > or approx. =10/sup -9.5/, which is remarkable large for such a low density cloud.

An abinitio and ion cyclotron resonance study of the protonation of borazine

The gas phase ion–molecule reactions and proton affinity of borazine have been investigated by both theoretical ab initio and ion cyclotron resonance techniques. The experimental proton affinity has been determined from competitive proton transfer equilibria with standard reference bases and found to be 196.4 ± 0.2 kcal/mol. Ion–molecule reaction schemes for reaction of borazine molecular ions have been proposed. Ab initio calculations find the proton affinity of borazine to be 203.4 kcal/mol and the most energetically favorable structure of the borazinium ion is one in which very little structural change occurs relative to neutral borazine with the exception of the geometry about the protonated nitrogen atom. Charge distributions and bond lengths are used to explain bonding changes upon protonation.

Observations of strongly deuterated molecules - Implications for interstellar chemistry

view Abstract Citations (37) References (16) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Observations of strongly deuterated molecules: implications for interstellar chemistry. Turner, B. E. ; Zuckerman, B. Abstract The J = 1 - 0 transitions of DCO(+), N2D(+), DCN, and DNC in 13 interstellar clouds has been surveyed. In the dark dust clouds L63 and L134N, the apparent ratio DCO(+)/HCO(+) exceeds unity. While the apparent ratio DNC/HNC is of order unity in these cluds, N2D(+)/N2H(+) is significantly smaller. In other sources outside the galactic center, DCO(+)/HCO(+) and DNC/HNC are typically a few hundredths and somewhat larger than DCN/HCN. None of these deuterated species is detected in the galactic-center region. These results are analyzed in terms of current ion-molecule reaction schemes. Possible differences between DCO(+)/HCO(+) and N2D(+)/N2H(+) are considered and used to place restrictions on physical conditions and abundances in deuterated sources. Predictions are made for NH2D/NH3 and HDO/H2O and compared with recent observations. Ion-molecule chemistry, as at present understood, appears consistent with existing observations of deuterated interstellar molecules. Publication: The Astrophysical Journal Pub Date: October 1978 DOI: 10.1086/182797 Bibcode: 1978ApJ...225L..75T Keywords: Cosmic Dust; Deuterium Compounds; Galactic Nuclei; Interstellar Chemistry; Abundance; Ionic Reactions; Molecular Interactions; Reaction Kinetics; Astrophysics; Deuterium:Interstellar Clouds; Interstellar Clouds:Molecules full text sources ADS |

Observations of interstellar sulfur monoxide

Millimeter-wave emission in the 1/sub 0/..-->..0/sub 1/, 2/sub 2/..-->..1/sub 1/, 3/sub 2/..-->..2/sub 1/, 2/sub 3/..-->..1/sub 2/, 4/sub 5/..-->..4/sub 4/, and 4/sub 3/..-->..3/sub 2/ transitions of /sup 32/SO and in the 3/sub 2/..-->..2/sub 1/ and 2/sub 3/..-->..1/sub 2/ transitions of /sup 34/SO is reported. A survey toward 18 sources shows that the galactic distribution of SO is similar to that of CS and H/sub 2/S. Declination-versus-velocity maps of the 2/sub 2/..-->..1/sub 1/, 3/sub 2/..-->..2/sub 1/, and 4/sub 3/..-->..3/sub 2/ transitions are used to study the anomalously large line widths near the Kleinmann-Low nebula. The /sup 34/SO lines are about as strong as predicted from the terrestrial abundance ratio /sup 34/S//sup 32/S. A map of the 3/sub 2/..-->..2/sub 1/ transition toward more than 100 points in rho Ophiuchi reveals two SO peaks of comparable intensity (one is approx.3'.5 northeast and the other is 15' southeast of the central peak in /sup 12/CO). SO emission in rho Ophiuchi occurs in a region where 6 cm H/sub 2/CO absorption is at a minimum. Predictions of line intensities are used to derive SO abundances in Orion A, NGC 2264, W49, and eight other sources. The SO column density is 9 or approx. =2 x 10/supmore » 14/ cm/sup -2/, except toward the Kleinmann-Low nebula, where the value is approx.10/sup 16/ cm/sup -2/. The H/sub 2/S to SO ratio agrees well with predictions based on an ion-molecule reaction scheme, but the CS to SO ratio may be higher than predicted by an order of magnitude.« less

Effects of low concentrations of O 2 and CO on the ion-clustering reactions in the lower ionosphere of Mars

It is demonstrated that under conditions which approximate those of the Martian ionosphere traces of CO and O 2 can be effectively incorporated in ion clusters via ion-molecule reaction schemes initiated by the CO 2 + ion. For example, when 0.3 % CO is added to CO 2, (CO) 2 + and [(CO) 2CO 2] + appear as the major cations (584 Å radiation, 300°K). In mixtures containing O 2 in addition to CO 2 (CO 2. O 2) + and [(CO 2) 2O 2] + are important species. A recently proposed mechanism to account for the low abundance of CO and O 2 in the Martian atmosphere is discussed in the light of these observations.

Ion–Molecule Reactions in Alpha-Particle Irradiated NH3, CD4, and D2O

We have investigated the time evolution of the various primary and secondary positive ion species formed in NH3, CD4, and D2O gases bombarded by 1- to 3.5-MeV alpha particles. The measurements were made with a pulsed time-of-flight mass spectrometer at pressures in the 10–40 micron range. Ion–molecule reaction schemes are proposed, the data analyzed for self-consistency, and a variety of reaction rates deduced. Comparisons are made with other experiments in which electron bombardment was used for primary ionization. Our results indicate the existence of a relatively long-lived [τ = 0.28(4)μsec] (C2D7+)* ion complex formed from the reaction CD3++CD4, paralleling previous results [R. A. Fluegge, J. Chem. Phys. 50, 4373 (1969)] for the CH4 system.

General Considerations Concerning Apparent Mobilities in Mixed Ion Populations: Drift Velocities of Mass-IdentifiedN+,N2+,N3+, andN4+Ions in Nitrogen

This paper summarizes the difficulties inherent in the measurement of ionic drift velocities in gases, emphasizing the need for careful control of the ionization conditions in the ion source and the necessity for mass analysis of the ions at the end of their flight path. Mass analysis provides a positive determination of the molecular composition of the ions reaching the detector, detects the possible presence of a mixture of charge carriers of various molecular compositions, and is essential to help determine whether or not the charge carriers which have a given molecular composition when they arrive at the detector have had that same composition throughout their transit through the drift region. If examination of the arrival-time spectrum shows that a detected species is involved in an ion-molecule reaction scheme such that the charge carrier has spent an appreciable portion of its total drift time in a different ionic form, then the "apparent drift velocity" derived from the measurement of the transit time and drift distance cannot be meaningfully compared with the existing theory. A drift-tube mass spectrometer used to study the drift of mass-analyzed ions is described, and experimental results are presented for nitrogen ions in the parent gas. The drift-tube pressures used here ranged from 0.05 to 0.25 Torr. The $\frac{E}{{p}_{0}}$ range covered was 7 to 50 V/cm Torr for ${\mathrm{N}}^{+}$ and ${\mathrm{N}}_{3}^{+}$ ions and was 7 to 70 V/cm Torr for ${\mathrm{N}}_{2}^{+}$ and ${\mathrm{N}}_{4}^{+}$ ions. The drift distance was varied from 9 to 34 cm. The transit-time spectra for ${\mathrm{N}}^{+}$ indicate that its drift velocities measured here are the "true" values characteristic of the ${\mathrm{N}}^{+}$ ion undergoing no reactive scattering collisions. The zero-field, reduced mobility of ${\mathrm{N}}^{+}$ in ${\mathrm{N}}_{2}$ is 2.47 ${\mathrm{cm}}^{2}$/V sec. Ion-molecule reactions involving the other ions prevented the determination of their true drift velocities, but the measured apparent drift velocities yield useful information about their drift behavior and the reactions linking the various ions.