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Results of a study in which fluorescence of the gamma system of nitric oxide was obtained by excitation from both the 2144 A line of ionized cadmium and a continuum source. Individual rotational lines of the 2144 A excited fluorescence spectrum were found to be partially polarized and to have polarizations of differ ing sign. Measured relative vibrational band intensities from line and continuum excitation were compared to calculated Franck-Condon factors. Those Franck-Condon factors based on a single potential for the two spin states of the X super pi state agreed better with measured values than those based on separate potentials for the two spin states. Calculated intensities of the v prime = 3 progression were used to calibrate the instrument response in the wavelength region from 2000 to 2500 A and were checked with measured intensities of the v prime = 0.1, and 2 progressions. Fluorescence of the epsilon and delta bands obtained with continuum lamp excitation also were compared to calculated intensities.
Franck-Condon factors calculated for vibrational energy level transitions in molecular hydrogen band systems
Auroral excitation rates and molecular vibrational tempratures in nitrogen 2PG from Franck-Condon factors obtained from intensity measurements and high resolution absorption spectral data
High-accuracy ab initio thermochemical predictions for the ionization energy of NF 3 , the barrier height (to inversion) of NF 3 + , and the dissociative ionization threshold of NF 3 to NF 2 + + F are presented and incorporated into Active Thermochemical Tables. The adiabatic ionization energy of the first ionization band of NF 3 , calculated at 12.647 ± 0.010 eV, is at odds with previous experimental interpretations by nearly 0.36 eV due to unfavorable Franck-Condon factors associated with this transition. The barrier (to inversion) height is calculated to be about 0.6 eV lower in energy than the prior interpretation, which instigates a discussion of the supposed vibrational structure of the first ionization band of NF 3 . Updated assignments of the photoelectron spectrum are proposed, and the loss in vibrational spacing on the high-energy side of the experimental ionization band is discussed. Rudimentary anharmonic Franck-Condon simulations qualitatively reproduce the broad spectral features observed in experiment.
Arylacetylides such as phenylacetylide (PhCC–, 1) are important nucleophiles used in synthetic chemistry yet rarely have they been studied as bare carbanions. In this work, the phenylacetylide anion was formed via electrospray ionization (ESI) or multistage mass spectrometry (MSn) experiments and subsequently examined in the gas phase by negative ion photoelectron spectroscopy (NIPES), ion-molecule reactions (IMR), alongside theoretical calculations to probe its fundamental structure and reactivity. Photoelectron spectra of PhCC– (1) revealed vertical (VDE) and adiabatic detachment energies (ADE), both of 3.220 eV. The latter value is also the electron affinity (EA) of the phenylethynyl radical (PhCC•) from which a bond dissociation energy (BDE) of phenylacetylene (PhCCH) was derived to be ca. 131.3 ± 1.7 kcal mol-1 using a gas-phase thermochemical cycle. Detachment of an electron from PhCC– at 266 nm likely results in resonant autodetachment, supported by Franck-Condon Factor (FCF) simulations. The phenylacetylide anion reacts with methyl iodide (CH3I) and allyl iodide (C3H5I) via SN2 nucleophilic displacement with measured rate coefficients of 4.29 and 3.66 × 10-10 cm3 molecule-1 s-1, respectively. The mechanisms associated with these displacement reactions are explained and understood in terms of the reaction kinetics, natural bond orbital (NBO) theory, and Density Functional Theory (DFT) calculations.
Tabulated sources of Franck-Condon factors and r-centroids for diatomic molecules
Quantum mechanical treatment of N and CO molecules, RKR Franck-Condon factors for gamma and beta band systems of NO, and wave functions and energy curves of LiH and BH
Transition probabilities for radiative lifetime of Swan and Mulliken diatomic C bands calculated from lifetime data using Franck-Condon factors
Isotope effects in Lyman and Werner systems of molecular hydrogen, HD and molecular deuterium, calculating band strengths, oscillator strengths and Franck-Condon factors
Measurement of a radiative lifetime of 9.6 (plus or minus 1.0) nsec for the SiO A(super 1)Pi state is reported. RKR Franck-Condon factors have been computed and, with these, absolute oscillator strengths are calculated. A band system at 3022 A has been found that may be due to SiO+, but the band is not resolved at our experimental resolution, and identification remains uncertain. The upper state of the carrier of this spectrum has a radiative lifetime of 8.3 (plus or minus 0.8) nsec.
The oscillator strengths for these SO transition band systems are calculated using RKR Franck-Condon factors and the radiative lifetime previously derived from electron-beam phase-shift measurements by Smith (1971). The SO transition concerned is of considerable astrophysical importance in the search for SO in the interstellar medium by means of space-based telescopes with monochromators since the transition probability is concentrated, as shown, in relatively few transitions from the ground state.
The probability of radiation producing ions in specific electronic and vibrational levels was documented. For example, when a narrow band-pass of solar ionizing photons is incident on an atmospheric species it is now possible to describe, accurately, how the radiant energy is shared among the various electronic states of the ions produced. The molecules studied were N2, CO, and CO2. These molecules were photoionized by radiation between 53 and 75 nm. The effects of autoionization are discussed and continuum vibrational intensities are tabulated and compared with theoretical Franck-Condon factors where available. The branching ratios and partial cross sections for ionization into various electronic states are tabulated.
Use of an electron-beam phase-shift apparatus to obtain the radiative lifetimes for vibrational levels of the SiO E 1 Sigma (+) state. It is found that the radiative lifetimes for the vibrational transitions of the E-X band are independent of the vibrational upper state. The measured phase shifts yield cascade free lifetimes of 10.5 plus or minus 1.1 nsec for v' from 1 to 7. Spectroscopic data from Elander and Lagerqvist (1971) were used to calculate potential curves by the Klein-Dunham procedure, and Franck-Condon factors and r-centroids for the transition were computed.
The paper reports on experimental vibrational intensity distributions for continuum photoionization of oxygen using both 584 and 304 A helium lines. A cylindrical mirror energy analyzer with known transmission properties was used to record photoelectron spectra at a resolution of 45 meV with dispersed He radiation. At each wavelength the vibrational intensity distribution were corrected for the transmission of the analyzer and normalized to 100 at the strongest level. A table lists the results with calculated Franck-Condon factors.
The vibrational intensity distribution of CO (a3 Pi - X1 Sigma+) Cameron bands was measured. Data combined from the present and from previous experiments suggest that a3 Pi vibrational temperatures are more characteristic of the parent molecule than are the details of the excitation mechanism. The temperatures were obtained using Franck-Condon factors to deconvolute the bands at 194, 199, and 206 nm. The values were 4800 K for CO2 and 1900 K for CO.
Tables of energy levels, Franck-Condon factors, r-centroids, transition moments, line wavelengths, and gf values are presented for the fourth positive system of CO.