Dean W. Robinson

The librational spectra of water and heavy water in crystalline salt hydrates

Abstract Infrared spectra are reported of nine mono- and dihydrates of alkali halides and alkaline earth halides. These spectra in the 300–600 cm−1 region are interpreted as arising from the librational modes of the bound water molecules as shown unambiguously by the frequency changes on substitution of deuterium oxide. Potential constants for this motion are given. Samples were prepared by evaporation of salt films in situ, and the method is seen to be of value for studying the limits of phase stability of unknown hydrates and related compounds. The number of bands observed in this region indicates for all cases studied the number of water molecules with different crystalline environments.

Mid‐ and Far‐Infrared Spectra of HF and DF in Rare‐Gas Matrices

The “vibration–rotation” and “pure rotation” spectra of HF and DF in rare‐gas matrices near 4°K have been studied, and assignments of the features due to the monomeric molecules have been made. The perturbations of the purely vibrational levels have been used to compute Lennard‐Jones parameters for the interaction between the polar molecule and its neighboring atoms. The center of action of the dispersion forces has been calculated for HF, and the rotational perturbations have been evaluated. The spectral absorption frequencies are rather well reproduced. It has been found that the experimental frequency shifts are not consistent with a theory of rotational–translational coupling but that they, and other “anomalous” spectral features, are predicted by considerations of the anisotropies in the rotational potential function.

Far‐Infrared Spectrum of Tetrahydrofuran: Spectroscopic Evidence for Pseudorotation

The infrared spectra of tetrahydrofuran and tetrahydrofuran‐d8 are reported between the limits 10 and 300 cm−1. The rather complex spectrum obtained for this molecule is interpreted in terms of the theory of pseudorotation of a puckered ring. The spectroscopically derived value of the parameter mq02 is (8.56±0.13)×10−40 g·cm2 for the ground, v=0, radial state and (8.48±0.15)×10−40 g·cm2 for the excited, v=1, radial state.

Electron binding to valence and multipole states of molecules: Nitrobenzene, para- and meta-dinitrobenzenes

Nitrobenzene anions (NB−) in both valence and dipole bound states are examined using laser (photodetachment) photoelectron and Rydberg electron transfer (RET) spectroscopies. Photoelectron spectroscopy of the valence NB− anion yields a valence (adiabatic) electron affinity of 1.00±0.01 eV. The reaction rates for charge transfer between atoms of cesium and xenon in high Rydberg states [Cs(ns,nd) and Xe(nf )] and NB exhibit a prominent peak in their n-dependencies consistent with the formation of a dipole bound anion having an electron affinity of 28 meV. Para-dinitrobenzene (pDNB) has a zero dipole moment and a large quadrupole moment. RET studies with pDNB show a complex n-dependence. The rate of formation of pDNB− ions exhibits a broad peak at low n-values and a second very broad feature extending to large n-values. The peak at low n is tentatively attributed to charge exchange into a quadrupole bound state (EAqb=25 meV). The absence of field-detachment for these ions suggests that if these are in a quad...

Zinc oxide and its anion: A negative ion photoelectron spectroscopic study

We have recorded, assigned, and analyzed the photoelectron spectrum of ZnO−. The adiabatic electron affinity (E.A.a) of ZnO and the vibrational frequencies of both ZnO and ZnO− were determined directly from the spectrum, with a Franck–Condon analysis of its vibrational profile providing additional refinements to these parameters along with structural information. As a result, we found that E.A.a(ZnO)=2.088±0.010 eV, ωe(ZnO)=805±40 cm−1, ωe(ZnO−)=625±40 cm−1, and that re(ZnO−)>re(ZnO) by 0.07 A. Since our measured value of E.A.a(ZnO) is 0.63 eV larger than the literature value of E.A.(O), it was also evident, through a thermochemical cycle, that D0(ZnO−)>D0(ZnO) by 0.63 eV. This, together with the literature value of D0(ZnO), gives a value for D0(ZnO−) of 2.24 eV. Since the extra electron in ZnO− is expected to occupy an antibonding orbital, the combination of D0(ZnO−)>D0(ZnO), ωe(ZnO−) re(ZnO) was initially puzzling. An explanation was provided by the calculations of Bauschlicher and...

Spectra of Matrix‐Isolated Water in the ``Pure Rotation'' Region

The infrared spectra of matrix‐isolated water in neon, argon, krypton, and xenon solids near 4°K have been obtained between 29 and 60 cm—1. The few lines that are observed depend strongly on the matrix material and are in good agreement with lines in the v1 and v2 vibrational bands. This observation confirms the widely held belief that the fine structure in the near‐infrared spectrum has a rotational or hindered‐rotational origin.

Ebert Spectrometer for the Far Infrared

An Ebert spectrometer is described with regard to its design, construction, and performance. It is intended cover the 500–20 cm−1 region, and has so far been tested between 500 and 150 cm−1, where a resolution of 0.5 cm−1 is uniformly attained. The advantages of the Ebert optics in the long wavelength infrared are that they lead to a compact, simple, and convenient instrument for this difficult region of the spectrum, the performance of which is at least equal to that of the more elaborate instruments.

Study of Some Electronic Transition Probabilities in CO and CN

The transition probabilities of the CO third positive (b 3Σ→a 3II), the CO Angstrom (B 1Σ+→A 1II), and the CN violet (B 2Σ+→X 2Σ+) systems have been obtained from measurements of radiative lifetimes by the phase‐shift method. In the CO Angstrom system the probability of B 1Σ+→A 1II was distinguished from the (greater) probability for B 1Σ+→X 1Σ+ by taking advantage of reabsorption (or resonance trapping) of the shorter wavelength radiation. In the CN (B 2Σ+→X 2Σ+) transition there is found to be no measurable dependence of the electronic transition moment on internuclear distance.

A pure‐rotational collisionally pumped OH laser

Laser oscillation is reported on certain pure‐rotational transitions in the ground electronic state of the hydroxyl ion, v=0 and v=1. the active medium has been prepared by the O(1D)+H2 reaction in a large excess of rare gas. The transitions on which oscillation occurs have upper states which are energetically resonant with one, or even two, vibrational quanta. The pumping mechanism is assigned as a V→R transfer with ΔJ the order of 12.

The OH and OD laser: Collision‐induced energy transfer pumping

Detailed studies of the relative intensities of pure rotational lasing in the v=0, 1, 2, 3 states of OH(2Π1/2) and the v=0, 1, 2, states of OD(2Π1/2) are presented. Differences in the laser patterns of these two molecules, such as variation in intensity maxima for specific J levels and double pulsed lasing phenomena, are explained on the basis of a computer simulation model incorporating R→T and V→R energy transfer mechanisms. The probability of collisionally induced R→T transitions is assumed to be given by exponential gap model in which the rotational parameter is evaluated by information theory (sum rule) approximations. The V →R relaxation is described in a two step process: first, the change of oscillator vibrational energy directly into oscillator rotational energy, and second, the absorption or removal of the energy defect (mismatch) by collisional R→T processes. The appropriate parameters for this transfer mechanism are also calculated with sum rule assumptions for the two molecules. The temporal ...