Fred Dale

Kinetic energy, temperature, and derived rotational temperature dependences for the reactions of Kr+(2P3/2) and Ar+ with HCl

Rate constants for the reactions of Kr+(2P3/2) with HCl and DCl and of Ar+ with HCl have been measured as a function of reactant ion/reactant neutral average center‐of‐mass kinetic energy (〈KEc.m.〉 ) at several temperatures. The measurements were made using helium as the carrier gas. From these data we have derived the dependences of the rate constants on the rotational temperature of H(D)Cl. Rate constants for the reaction of Kr+(2P1/2) with HCl have also been measured as a function of temperature. The rate constants for all of the reactions were found to decrease with increasing temperature. The rate constants were also found to decrease with increasing 〈KEc.m.〉 at low 〈KEc.m.〉 but then to increase at higher 〈KEc.m.〉 . A significant rotational temperature dependence of the rate constant was derived for the reaction of Kr+(2P3/2) with H(D)Cl. The analogous derivation for Ar+ reacting with HCl showed the rate constant for this reaction to be independent of the rotational temperature of HCl within experime...

Proton transfer reactions of H+(H2O)n=2–11 with methanol, ammonia, pyridine, acetonitrile, and acetone

We report here the first measurements of rate constants involving cluster ions with more than five ligands. We have measured rate constants, or lower limits to rate constants, for the reactions of H+(H2O)n=2–11 with NH3, CH3CN, CH3OH, CH3COCH3, and C5H5N (pyridine). The experimental techniques needed to study these ions and neutrals at low temperatures are described. The reactions all proceed rapidly by proton transfer with varying degrees of ligand transfer. At low temperatures the rate constants are larger than the collision rate constant based on an ion–dipole potential. Reasons for this are examined. Thermal dissociation appears to control the size distribution of the primary ion clusters and to affect the observed product distribution.

Photodissociation of positive ions. I. Photodissociation spectra of D+2, HD+, and N2O+

The operation of an apparatus constructed to measure absolute photodissociation spectra of ions and to determine the kinetic energy spectrum of the photoproducts by time‐of‐flight analysis is described. Photodissociation spectra for the processes D+2+hν→D++D and N2O+→NO++N have been obtained, and the photodissociation cross sections for HD++hν→H++D and HD++hν→D++H have been measured. The photodissociation spectrum of D+2, using an irradiation bandwidth of <0.05 to 0.1 nm, is in reasonable agreement with the structureless spectrum of von Busch and Dunn obtained with a 20 nm bandwidth. The two possible photoprocesses in HD+ were observed to have the same cross sections 2×10−19 cm2 at 589 nm. The photodissociation spectrum of N2O+ over the range 295–342 nm was found to be very sharply structured, with σNO+ =2.6×10−18 cm2 for the largest peak, at 338.5 nm. Fifteen peaks in the N2O+ spectrum were assigned to vibrational progressions in the ? 2Σ←? 2Π1/2,3/2 transition. In making the assignments it was necessary...

Flowing afterglow apparatus for the study of ion-molecule reactions at high temperatures

We describe two versions of a high temperature flowing afterglow apparatus. With a stainless steel flow tube wrapped with heating tape we have obtained data over the range 300–1300 K. In a version with a ceramic flow tube in a commercial furnace we have obtained data over the range 300–1600 K. The ceramic version is designed to take data up to 1800 K, but we have encountered experimental problems at the upper temperature range. The design modifications to a standard flowing afterglow needed to make measurements at elevated temperatures are described in detail, as are problems associated with operating at elevated temperatures. Samples of data are given.

Collisional vibrational quenching of NO+(v) ions

Vibrational quenching rate constants have been measured for NO+(v>0) ions with 15 neutral quenching molecules by the SIFDT‐monitor ion technique. The temperature dependence of the quenching rate constants for the reactions of the neutrals N2, CO2, and CH4 has been investigated from 208 to 450 K. The dependence of the CH4 quenching rate constant on collision energy has been determined in the energy range 0.03–0.12 eV at 208 and 296 K. Also measured are rate constants for some of the reactions pertinent to the monitor ion technique.

Study of ion—neutral reactions with a time-of-flight double mass spectrometer

Abstract The times-of-flight of reactant and product ions from some low energy ion—neutral reactions are measured using a longitudinal double mass spectrometer system. This system consists of a 2.54 cm 90 degree magnetic sector ion beam selector, a collision chamber and grid system, and a 46 cm quadrupole mass filter, together with a multichannel scaler, operated at dwell times of 50 nanosec per channel, that serves as a flight-time recorder. Reactant ions are produced as a pulsed beam by applying 0.1 to 1.0 microsec pulses to an electron control grid. The time-of-flight of these ions to the collision chamber is obtained by measuring the delay between the pulse on the electron control grid and a pulse applied to a grid close to the collision chamber used to stop the reactant ion beam. Times-of-flight of the reactant and product ions through the collision chamber, grid system, and mass filter are then obtained by difference. The apparatus has been used to study ion—neutral reactions in the range of reactant ion energies from 0.3 to 250 eV and of product ion energies from thermal to about 150 eV. Consideration of the sources of error indicates that the system is most useful for the range of ion energies from thermal to a few tens of eV. Results obtained in the study of three ion—neutral reactions are presented. These are Ar++Ar+→Ar+Ar+,CO+2+CO2→CO2+CO+2, and CO++CO2→CO+CO+2.

Reactions of OH−⋅H2O with NO2

Cross sections for reactions of OH−⋅H2O with NO2 are reported for interaction energies from 0.2 to 6 eV. Reactions producing the ions HNO3− and NO2−⋅H2O were observed, in addition to charge transfer and collisional dissociation. These reactions were not observable at an interaction energy of 0.04 eV. Based upon these results, upper and lower bounds for the electron affinity of HNO3 are 0.39⩽E.A. (HNO3)⩽0.73 eV and for the bond dissociation energy of NO2−–H2O are 0.1⩽D(NO2−–H2O) 0.6 eV. It is suggested that the strong energy dependence of the cross sections for the reactions forming HNO−3 and NO2−⋅H2O is the result of dissociation of these ions before detection.

Production of vibrationally excited O+2 in the reaction of O+ with CO2

The production of vibrationally excited O+2 in the reaction of O+ with CO2 has been studied as a function of temperature. The measurements were made in a variable temperature‐selected ion flow drift tube by the monitor ion technique. The principal vibrational level produced is found to be O+2(v=1), with approximately 45%–51% of the O+2 produced in this state. The remainder is O+2(v=0), representing 23%–43%, and O+2(v≥2), representing 6%–32%. More vibrational excitation is observed at higher temperature, but this temperature dependence may be obscured due to vibrational quenching. The various vibrational levels of O+2 observed here were found to react with Xe at different rates, with O+2(v=1) having the largest rate constant. Rate constants for several reactions pertinent to this study are also reported.

The photodissociation spectrum of SO+2

The photodissociation spectrum of SO+2 corresponding to the process SO+2 +hν→SO++O has been measured on a triple quadrupole system for the wavelength ranges: 3000–3400 and 4400–5120 A. The spectrum in the visible has been assigned to the C 2B1←A 2A2 transition and vibrational structure analyzed to yield λ00=4187 A, the harmonic vibrational frequencies ν’1=953 cm−1, ν’’2=499 cm−1, ν’1=767 cm−1, and ν2 =410 cm−1, and the anharmonicity constants X‘11 =−6.3 cm−1, X’’12 =−6.1 cm−1, X‘22 =−4.2 cm−1, X12 =−6.3 cm−1, and X’22 =−7.4 cm−1. Apparent photodissociation cross sections ranged from ∼1×10−20–1.6×10−19 cm2 in the visible spectrum. In the UV spectrum the highly congested vibrational structure could not be resolved sufficiently for analysis; photodissociation cross sections ranged from ∼2–4×10−19 cm2 with broad bands roughly corresponding to expected progression in ν1 and ν’2 within the C 2B1←X 2A1 electronic transition. The process SO+2 +hν→S++O2 showed an onset near 3108 A and the corresponding pho...

Vibrational Quenching of NO+(V) Ions in Collision with H2, D2 and O2

The vibrational quenching rate constants for NO+(v), predominantly in the v=1 state, have been measured at 200 and 293 K in collisions with H2 and D2 and at 200, 293, and 458 K with O2. The rate constants are all very low, corresponding to quenching probabilities ∼10−4. The low rate constants reflect very shallow attractive potential wells. In the case of H2 and D2 this is a consequence of their low polarizabilities. In the case of O2, repulsive chemical interactions offset the electrostatic attraction to yield a shallow attractive well. This is a consequence of the singlet NO+ and triplet ground state O2 not approaching on the attractive NO+3 ground state potential surface, which is a singlet. The temperature dependences of the quenching rate constants are generally slight, indicating that the collision energies are in a range comparable to the attractive well depth and that the quenching is not strongly dominated by either the attractive forces, which would give a negative energy dependence, or by the r...