THE HYDROGEN–CHLORINE SYSTEM IN THE MM PRESSURE RANGE II. THE VIBRATIONAL GROUND STATE STUDIED BY SELF-ABSORPTION

1964 ◽  
Vol 42 (10) ◽  
pp. 2193-2200 ◽  
Author(s):  
J. R. Alrey ◽  
F. D. Findlay ◽  
J. C. Polanyi
Keyword(s):  
Excited States ◽  
Relative Intensity ◽  
Ground State ◽  
Pressure Range ◽  
Infrared Emission ◽  
Absolute Amount ◽  
Reaction Products ◽  
Vibrationally Excited ◽  
Vibrational Ground State ◽  
Apparent Deviation

Studies of energy distribution among reaction products, through the agency of infrared chemiluminescence, have previously only yielded information concerning the distribution among vibrationally excited states. In the work described here it was shown that self-absorption of the infrared emission could be used as a measure both of the relative and the absolute amount of product present in the vibrational ground state, ν = 0. Two independent methods were used to measure the extent of self-absorption. The first method relied on measurements of an apparent deviation from Boltzmann-type rotational intensity distribution within the ν(1–0) and ν(2–1) bands. The second method depended on measurements of an apparent deviation of the relative intensity of corresponding H35Cl and H37Cl isotopic lines from the natural abundance ratio. (It was shown, at the same time, that the isotopic reactions H + 35Cl2 → H35Cl + 35Cl and H + 37Cl2 → H37Cl + 37Cl have the same rate constant, within ±10%). A third method of measuring the extent of self-absorption, which depends on the detection of an anomaly in the relative intensity of P- and R-branch emission lines is discussed.The self-absorption method was applied to the study of the hydrogen–chlorine system in the 1–2 mm Hg pressure range (see also Part I). Mean partial pressures of HClν=0 ~ 10−2 mm Hg were measured in individual rotational states to an accuracy of ca. ±10%, using an optical path length of 20 cm. The rotational distribution in ν = 0 corresponded to a temperature of 1150 ± 150 °K (the uncertainty in this figure encompasses two independent methods of estimating the self-absorption), as compared with 1300 ± 100 °K for all vibrationally excited states (Part I).

High-Resolution Vibrational Spectra of Furazan

1991 ◽  
Vol 46 (10) ◽  
pp. 841-850
Author(s):  
Otto L. Stiefvater
Keyword(s):  
Excited States ◽  
Ground State ◽  
Double Resonance ◽  
Microwave Spectroscopy ◽  
Statistical Uncertainty ◽  
Molecular Constants ◽  
Vibrationally Excited ◽  
Vibrational Ground State ◽  
Vibrational Bands ◽  
Ft Ir

AbstractThe study by Fourier transform (FT) infrared (IR) spectroscopy of the fundamental vibrational bands v12 and v5 of furazan yields the origins of these bands with a statistical uncertainty of 10-6 cm-1, which leads to an estimated absolute uncertainty of 10-4 cm-1. The values are v°12 = 952.6123 cm -1 and v°5 = 1.005.3536 cm -1. They confirm the values previously deduced from laser/microwave double resonance (LMDR) experiments. Previous results for the molecular constants of the vibrational ground state and of the two vibrationally excited states, as obtained by double resonance modulation (DRM) microwave spectroscopy alone, are confirmed and refined. Advantages brought about through the combination of the DRM microwave and the FT-IR technique are outlined.

The microwave spectrum and molecular structure of trimethylene sulphoxide; bends, tilts and twists in the methylene groups

1977 ◽  
Vol 354 (1679) ◽  
pp. 491-509 ◽  
Keyword(s):  
Excited States ◽  
Ground State ◽  
Rotational Spectrum ◽  
Vibrationally Excited ◽  
Rotational Constants ◽  
Vibrational Ground State ◽  
Isotopic Species ◽  
Microwave Rotational Spectrum ◽  
Methylene Groups ◽  
The Common

The microwave rotational spectrum of the common isotopic species ( 12 CH 2 ) 32 3 S 16 O of trimethylene sulphoxide has been assigned and rotational constants obtained for the vibrational ground state, the first four excited states of the ring puckering mode and two other low-lying vibrationally excited states. In addition rotational constants have been derived for the vibrational ground state of each of the eight different singly substituted isotopic species [ 34 S], [ 13 C 2 ], [13 C 3 ], [ 2 H 2 ], [ 2 H 2 .], [ 2 H 3 ], [ 2 H 3 .] and [ 18 O], with the first three in natural abundance, and are as follows:

Microwave Spectra of Furazan. IV. Rotation Spectra of Vibrationally Excited States of Perdeuterated Furazan

1990 ◽  
Vol 45 (9-10) ◽  
pp. 1131-1143
Author(s):  
Otto L. Stiefvater
Keyword(s):  
Ir Spectroscopy ◽  
Excited States ◽  
Relative Intensity ◽  
Ground State ◽  
Double Resonance ◽  
Microwave Spectroscopy ◽  
Vibrationally Excited ◽  
Pure Rotation ◽  
Intensity Measurements ◽  
Modes Of Vibration

Abstract The pure rotation spectra of molecules in 25 vibrationally excited states of perdeuterated furazan, C2D2N2O, have been studied by double resonance modulation (DRM) microwave spectroscopy. Twelve of these spectra have been correlated, -on the basis of relative intensity measurements under DRM -, with fundamental vibrations as previously established by IR spectroscopy. Rotational parameters for these 12 fundamental levels are reported, and the contributions to the effective rotational constants and to the inertia defect of the ground state of d2 -furazan have been determined for 10 modes of vibration.

Excited-State Dynamics in the RNA Nucleotide Uridine 5’-Monophosphate Investigated by Femtosecond Broadband Transient Absorption Spectroscopy

2019 ◽  
Author(s):  
Matthew M. Brister ◽  
Carlos Crespo-Hernández
Keyword(s):  
Excited State ◽  
Excited States ◽  
Ground State ◽  
Transient Absorption ◽  
Electronic Energy ◽  
Transient Absorption Spectroscopy ◽  
Electronic Relaxation ◽  
Vibrationally Excited ◽  
Excited State Dynamics ◽  
Π State

<p></p><p> Damage to RNA from ultraviolet radiation induce chemical modifications to the nucleobases. Unraveling the excited states involved in these reactions is essential, but investigations aimed at understanding the electronic-energy relaxation pathways of the RNA nucleotide uridine 5’-monophosphate (UMP) have not received enough attention. In this Letter, the excited-state dynamics of UMP is investigated in aqueous solution. Excitation at 267 nm results in a trifurcation event that leads to the simultaneous population of the vibrationally-excited ground state, a longlived <sup>1</sup>n<sub>O</sub>π* state, and a receiver triplet state within 200 fs. The receiver state internally convert to the long-lived <sup>3</sup>ππ* state in an ultrafast time scale. The results elucidate the electronic relaxation pathways and clarify earlier transient absorption experiments performed for uracil derivatives in solution. This mechanistic information is important because long-lived nπ* and ππ* excited states of both singlet and triplet multiplicities are thought to lead to the formation of harmful photoproducts.</p><p></p>

scholarly journals The Microwave Spectrum of 3,4-Dihydro-1,2-Pyran

1985 ◽  
Vol 40 (9) ◽  
pp. 913-919
Author(s):  
Juan Carlos López ◽  
José L. Alonso
Keyword(s):  
Dipole Moment ◽  
Excited States ◽  
Ground State ◽  
Principal Axis ◽  
Microwave Spectrum ◽  
Average Intensity ◽  
Ring Conformation ◽  
Vibrationally Excited ◽  
Rotational Constants ◽  
Displacement Measurements

Abstract The rotational transitions of 3,4-dihydro-1,2-pyran in the ground state and six vibrationally excited states have been assigned. The rotational constants for the ground state (A = 5198.1847(24), B = 4747.8716(24) and C = 2710.9161(24) have been derived by fitting μa, μb and μc-type transitions. The dipole moment was determined from Stark displacement measurements to be 1.400(8) D with its principal axis components |μa| =1.240(2), |μb| = 0.588(10) and |μc| = 0.278(8) D. A model calculation to reproduce the ground state rotational constants indicates that the data are consistent with a twisted ring conformation. The average intensity ratio gives vibrational separations between the ground and excited states of the ring-bending and ring-twisting modes of ~ 178 and ~ 277 cm-1 respectively.

Preferred Rotameric Conformations of Isobutyraldehyde, Their Dipole Moments and Vibrationally Excited States by Microwave Spectroscopy

1986 ◽  
Vol 41 (3) ◽  
pp. 483-490 ◽  
Author(s):  
O. L. Stiefvater
Keyword(s):  
Oxygen Atom ◽  
Excited States ◽  
Ground State ◽  
Dipole Moments ◽  
Microwave Spectroscopy ◽  
Centrifugal Distortion ◽  
Gauche Conformation ◽  
Vibrationally Excited ◽  
Trans Conformation ◽  
Centrifugal Distortion Constants

The earlier prediction of the preferred and the less stable rotameric conformations of isobutyraldehyde, (CH3)2CHCHO, has been confirmed experimentally by microwave spectroscopy. The compound exists mainly in a gauche conformation, in which one of the methyl groups is eclipsed by the oxygen atom, and the less stable rotamer is the trans conformation, in which the oxygen atom eclipses the isopropyl hydrogen.Ground state rotational constants (in MHz) and centrifugal distortion constants (in kHz), together with dipole moments (in D), are:Rotation spectra due to three torsionally excited states of each rotamer have been identified, along with satellites arising from CH3 internal rotation and CC2 wagging.

THE HYDROGEN–CHLORINE SYSTEM IN THE MM PRESSURE RANGE: I. ENERGY DISTRIBUTION AMONG VIBRATIONALLY EXCITED STATES

1964 ◽  
Vol 42 (10) ◽  
pp. 2176-2192 ◽  
Author(s):  
F. D. Findlay ◽  
J. C. Polanyi
Keyword(s):  
Excited States ◽  
Rotational Temperature ◽  
Relative Rate ◽  
Infrared Emission ◽  
Vibrational States ◽  
Vibrationally Excited ◽  
Experimental Conditions ◽  
Reduced Pressure ◽  
A Chain ◽  
First Time

When atomic plus molecular hydrogen coming from a Wood's discharge tube are mixed with molecular chlorine, infrared emission is observed (1). At low reagent pressures, ~10−2 mm Hg, this emission can be related to the relative rate of the reaction H + Cl2 → HCl†ν + Cl proceeding to form HCl in vibrationally excited states ν = 1–6, of the ground electronic state. In the present work this system has been investigated for the first time at ~100 × the reagent pressure (~1 mm Hg). The reaction was shown to proceed by a chain mechanism. The translational–rotational temperature was 1300 ± 100 °K under the experimental conditions normally used. The vibrational distribution was notable for the presence of vibrators in levels ν = 7 and 8, which are respectively 4 and 10 kcal higher in energy than the exothermicity of the H + Cl2 reaction. The population in these levels appeared to be related to that in the levels with [Formula: see text]; it was proposed that vibrational–vibrational exchange among these lower levels was responsible for populating the higher ones. A simple model yielded a collision efficiency for HCl†ν=1 + HCl†ν=6 → HCl†ν=7 + HCl†ν=0, of Z1,6t = 6 × 103 collisions per transfer. Addition of HCl to the reaction mixture brought about a redistribution among vibrationally excited states indicative of a fast vibrational transfer, HClν=0 + HCl†ν=2 → 2 HCl†ν=1.At reduced pressure of HCl† the stationary-state distribution among higher vibrational states approximated closely to that observed at 10−2 mm Hg total pressure (where collisional deactivation is insignificant), suggesting that collisional deactivation was not of major importance even at the pressure used in the present work. In order to account for the high translational–rotational temperature, in the absence of substantial vibrational deactivation, it was necessary to suppose that the greater part of the energy liberated by the reaction H + Cl2 went directly into translational and rotational motion of the products.

scholarly journals Do vibrationally excited OH molecules affect middle and upper atmospheric chemistry?

2010 ◽  
Vol 10 (20) ◽  
pp. 9953-9964 ◽  
Author(s):  
T. von Clarmann ◽  
F. Hase ◽  
B. Funke ◽  
M. López-Puertas ◽  
J. Orphal ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Ground State ◽  
Atomic Oxygen ◽  
Vibrational Excitation ◽  
Reaction Rates ◽  
Effective Rate ◽  
Rate Coefficients ◽  
Vibrationally Excited ◽  
Vibrational Ground State ◽  
Odd Oxygen

Abstract. Except for a few reactions involving electronically excited molecular or atomic oxygen or nitrogen, atmospheric chemistry modelling usually assumes that the temperature dependence of reaction rates is characterized by Arrhenius' law involving kinetic temperatures. It is known, however, that in the upper atmosphere the vibrational temperatures may exceed the kinetic temperatures by several hundreds of Kelvins. This excess energy has an impact on the reaction rates. We have used upper atmospheric OH populations and reaction rate coefficients for OH(v=0...9)+O3 and OH(v=0...9)+O to estimate the effective (i.e. population weighted) reaction rates for various atmospheric conditions. We have found that the effective rate coefficient for OH(v=0...9)+O3 can be larger by a factor of up to 1470 than that involving OH in its vibrational ground state only. At altitudes where vibrationally excited states of OH are highly populated, the OH reaction is a minor sink of Ox and O3 compared to other reactions involving, e.g., atomic oxygen. Thus the impact of vibrationally excited OH on the ozone or Ox sink remains small. Among quiescent atmospheres under investigation, the largest while still small (less than 0.1%) effect was found for the polar winter upper stratosphere and mesosphere. The contribution of the reaction of vibrationally excited OH with ozone to the OH sink is largest in the upper polar winter stratosphere (up to 4%), while its effect on the HO2 source is larger in the lower thermosphere (up to 1.5% for polar winter and 2.5% for midlatitude night conditions). For OH(v=0...9)+O the effective rate coefficients are lower by up to 11% than those involving OH in its vibrational ground state. The effects on the odd oxygen sink are negative and can reach −3% (midlatitudinal nighttime lowermost thermosphere), i.e. neglecting vibrational excitation overestimates the odd oxygen sink. The OH sink is overestimated by up to 10%. After a solar proton event, when upper atmospheric OH can be enhanced by an order of magnitude, the excess relative odd oxygen sink by consideration of vibrational excitation in the reaction of OH(v=0...9)+O3 is estimated at up to 0.2%, and the OH sink by OH(v=0...9)+O can be reduced by 12% in the thermosphere by vibrational excitation.

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