A. B. F. Duncan

Lifetime Measurements of Some Excited States of Nitrogen, Nitric Oxide, and Formaldehyde

An experimental method for measurement of short decay times of fluorescence (10—8—10—5 sec) from excited states of molecules is described. The method is applied to the transitions C3IIu—B3IIg (second positive) and B3IIg—A3Σu+ (first positive) of nitrogen and to the transitions A2Σ+—X2II (γ system) and B2II—X2II (β system) of NO. Direct measurement of the lifetime of the lowest singlet excited state of formaldehyde is reported. In some of the transitions, the dependence of lifetime on vibrational quantum number in the initial upper state were studied. The pressure dependence of the lifetimes was also investigated.

Fluorescence of Nitrogen Dioxide

The mean lifetime of fluorescence of NO2 vapor was measured at pressures in the range 12 to 0.6 microns by a direct electronic method. A linear dependence of lifetime on pressure was found, and extrapolation to zero pressure gave 44 microseconds for the lifetime in absence of collisions. The fluorescence spectrum in the region 4600—8000 A was photographed with 4358 and 5461 A excitation, with somewhat different results. Interpretation of the results appears to require two excited electronic levels, one of which is not connected optically with the normal state and which is responsible for the long‐lived fluorescence.

Electronic Structure of Ammonia

A self‐consistent field calculation of the normal state of the ammonia molecule is made in the molecular orbital approximation. The molecular orbitals are expressed as linear combinations of all valence and inner shell orbitals of the atoms, and all interactions of the ten electrons are included. The total molecular energy, —56.096 au, is 99.2% of the experimental value. The dissociation energy, 0.3308 au, is about 72% of the experimental value. The calculated dipole moment (1.486 Debye) is almost equal to the experimental value (1.46D). The two lowest ionization potentials are calculated as 9.94 and 16.20 ev, and are probably within one ev of the experimental values. An equivalent orbital representation is obtained from the molecular orbitals and directional features of distribution of electron density are discussed. The integrals over atomic orbitals were all evaluated by standard mathematical methods, which is discussed in an appendix.

Mean Lifetime of the Fluorescence of Acetone and Biacetyl Vapors

The effects of pressure, temperature, and exciting intensity on the lifetime of fluorescence of acetone and biacetyl vapor have been investigated. The pressure dependence of the lifetime in acetone was interpreted in terms of the formation of double molecules, and part of the temperature dependence was interpreted in terms of the formation of double molecules. The lifetime in biacetyl was found to be independent of pressure at a constant temperature, but dependent on temperature. The effect of oxygen on the lifetime in biacetyl was explained by assuming a simple Stern‐Volmer mechanism for quenching. The lifetimes of fluorescence in both acetone and biacetyl were found to be dependent on the incident intensity. This effect was explained by assuming that the fluorescing molecules of both compounds were quenched by the products of photochemical decomposition.

Electronic Spectrum of Carbonyl Fluoride

The complete electronic spectrum of carbonyl fluoride has been observed for the first time down to 1215 A. At least four electronic transitions occur in this spectral region. The first three electronic transitions are associated with elaborate vibrational structures, which are analyzed. The transitions are interpreted as two n → π* types and one n → σ* type. A π → π* type transition is found at shorter wavelengths. Other unresolved transitions occur at still shorter wavelengths where the intensity increases continuously to the limit of observation. The ionization potential of carbonyl fluoride has been determined by electron impact in a mass spectrometer as 13.17 ± 0.1 eV.

The Absorption Spectrum of Sulfur Hexafluoride in the Vacuum Ultraviolet Region

The spectrum of sulfur hexafluoride has been investigated down to wavelengths about 600A. The maximum of the first electronic transition is found at about 1050A. Three other transitions occur between this wavelength and 802A, where strong continuous absorption begins, and nothing further can be resolved at shorter wavelengths. Qualitative suggestions are offered about the dissociation of SF6 and the value of its ionization potential.

Mean Lifetime of the Lowest Excited Singlet State of Benzene

The lifetime of the first excited 1B2u state of benzene has been determined from measurement of decay of fluorescence in the vapor phase. High‐frequency electrical excitation, rather then optical excitation was used. The pressure dependence of the lifetime has been studied under different conditions. The lifetime extrapolated to zero pressure is 0.59 μsec. The pressure dependence is interpreted by a mechanism of collisional deactivation.

Calculations on Rydberg Terms of the Water Molecule

Calculations are reported on Rydberg series terms of the water molecule and are compared with available experimental data. A one‐center core function is assumed, based on a model of Banyard and March. Trial one‐electron Rydberg functions are assumed to be mutually orthogonal and orthogonal to the core function. The one‐electron energies are obtained from a potential which contains operators for the core electrons. The calculated terms are obtained with an average accuracy of about one percent or less except for lowest members of some series. Variation of terms with respect to screening parameters led to stationary values of terms in all cases.

The Absorption Spectrum of Ethylene Oxide in the Vacuum Ultraviolet

The spectrum of ethylene oxide was investigated from the visible down to about 600A, with high resolution in the vacuum region. No discontinuous absorption was found above 1713A. Two Rydberg series, beginning at 1435 and 1382A were found, which converge to the same ionization potential at about 10.81 ev. Two non‐Rydberg transitions were found, with origins apparently at 1713.4 and 1572.4A. An analysis and discussion is made of the spectrum. It is concluded that the Rydberg transitions arise by excitation from a molecular bonding orbital, very similar to one responsible for Rydberg series in ethylene and related compounds.

The Spectrum of Deuteroacetone in the Vacuum Ultraviolet A Comparison with the Spectrum of Acetone

The spectrum of acetone‐d6 of over 90 percent purity has been photographed in the region 2000–1300A, with a dispersion of 4.14A per mm. Data for the transition at about 51,000 cm−1 are presented together with new data on acetone in the same region. A discussion of the normal state of the acetones is given, and an analysis is made of the electronic spectra. It is shown that no vibrational frequency near 1200 cm−1 appears in the excited state of acetone‐d6 and that this frequency in acetone cannot be ascribed to the C–O vibration.