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C. G. Stevens

Bio: C. G. Stevens is an academic researcher from Columbia University. The author has contributed to research in topics: Rotational–vibrational spectroscopy & Fermi resonance. The author has an hindex of 2, co-authored 2 publications receiving 145 citations.

Papers
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Journal ArticleDOI
TL;DR: In this paper, the authors used a narrow band, pulsed dye laser in the region between 5934 and 5940 A to obtain a partial rotational analysis of a K = 0 subband of a 2 B 2 ← 2 A 1 transition.

87 citations

Journal ArticleDOI
TL;DR: The C-H stretch overtone spectra of methane, ethylene, propane, cyclopropane and isobutane (5.0 and 6.0) have been obtained at temperatures between 143 and 189 K as discussed by the authors.
Abstract: The C–H stretch overtone spectra of methane (5–0), ethylene (5–0 and 6–0), ethane (5–0 and 6–0), propyne (4–0 and 5–0 acetylenic and 5–0 methyl C–H stretches), allene (5–0), propane (5–0 and 6–0), cyclopropane (5–0 and 6–0), dimethyl ether (5–0), and isobutane (5–0) have been recorded at temperatures between 143 and 189 K, depending on the molecule. A comparison is made to the spectra obtained at room temperature, with the goal of improved understanding of the band shapes. The temperature dependence of most of the observed bands is found to be significantly less than that expected for ‘‘simple’’ bands. For these small to medium size hydrocarbons, the temperature independence of the overtone bands is found to correlate loosely with the density of states and with the degree of saturation. Other factors are important determinants of spectral widths and temperature independence as well, such as conformational inequivalence of the C–H oscillators, and the number and positions of the oscillators. It is concluded that the vast majority of hydrocarbon C–H stretch high overtone bands have upper states which are extensively mixed with other states. This is the case even for most of the relatively small hydrocarbons. This mixing produces a broadening effect and greatly increases the transition density, thereby diluting the oscillator strength of the rovibrational transitions from that of the zero‐order approximation. The Fermi resonance type of interaction appears to be of greater importance than the Coriolis type in determining the appearance of the high overtone bands.

58 citations


Cited by
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Journal Article
TL;DR: Theorie des effets de couplage vibronique multimodes is described in this paper, where couplages mettant en jeu des modes and des etats degeneres.
Abstract: Mise au point. Theorie des effets de couplage vibronique multimodes. Probleme a 2 etats. Couplage vibronique mettant en jeu des modes et des etats degeneres. Effets du couplage vibronique multimodes en spectroscopie. Comportement statistique des niveaux d'energie vibroniques. Intersections coniques et evolution temporelle de la fluorescence

1,424 citations

Journal ArticleDOI
TL;DR: In this article, a multiconfiguration self-consistent field (MC-SCF) wavefunctions have been computed for the low-lying X 2A1, A 2B2, B 2B1, C 2A2, 4B2 and 2Σ+g electronic states of NO2.
Abstract: Traditional spectroscopic analysis of the complex and irregular absorption spectrum of NO2 has provided a relatively small amount of information concerning the nature of the excited states. An extensive ab initio investigation has been undertaken, therefore, to provide a basis for interpretation of the experimental results. Multiconfiguration self‐consistent‐field (MC–SCF) wavefunctions have been computed for the low‐lying X 2A1, A 2B2, B 2B1, C 2A2, 4B2, 4A2, and 2Σ+g electronic states of NO2. The minima of the A 2B2, B 2B1, and C 2A2 states have all been found to be within 2 eV of the minimum of the X 2A1 ground state; for these states, C2v potential surfaces have been constructed for purposes of a spectral interpretation. The 4B2, 4A2, and 2Σ+g states are all more than 4 eV above the minimum of the ground state and have been examined in less detail. The study described here significantly improves on previous NO2 ab initio calculations in three important areas: (1) The double‐zeta‐plus‐polarization quality basis set is larger and more flexible; (2) the treatment of molecular correlation is more extensive; and (3) the electronic energies have been calculated for several different bond lengths and bond angles in each state. For the four lowest doublet states the following spectral data have been obtained: The ground state experimental constants are included in parentheses. The estimated accuracy of the various parameters is ±0.02 A for bond length, ±2° for bond angle, ±10% for the vibrational frequencies, ±0.10 D for dipole moments, and ±0.3 eV for the adiabatic excitation energies. An unusual feature has been found for the 2Σ+g state. The equilibrium geometry of this linear state has two unequal bond lengths of 1.20 A and 1.42 A and the inversion barrier is approximately 800 cm−1.

253 citations

Journal ArticleDOI
21 Mar 2008-Science
TL;DR: It is demonstrated that the reaction of electronically excited nitrogen dioxide with water can be an important source of tropospheric hydroxyl radicals, and inclusion of this chemistry is expected to affect modeling of urban air quality.
Abstract: Hydroxyl radicals are often called the “detergent” of the atmosphere because they control the atmosphere9s capacity to cleanse itself of pollutants. Here, we show that the reaction of electronically excited nitrogen dioxide with water can be an important source of tropospheric hydroxyl radicals. Using measured rate data, along with available solar flux and atmospheric mixing ratios, we demonstrate that the tropospheric hydroxyl contribution from this source can be a substantial fraction (50%) of that from the traditional O(1D) + H2O reaction in the boundary-layer region for high solar zenith angles. Inclusion of this chemistry is expected to affect modeling of urban air quality, where the interactions of sunlight with emitted NOx species, volatile organic compounds, and hydroxyl radicals are central in determining the rate of ozone formation.

241 citations

Journal ArticleDOI
TL;DR: In this article, the A 2 A 1 state has a propensity for being formed in high K a rotational levels v 2 vibrational levels, with an average vibrational energy content of 1000 cm −1.

153 citations