Rotational line intensities in 3Σ–1Σ electronic transitions

1968 ◽  
Vol 46 (14) ◽  
pp. 1637-1643 ◽  
Author(s):  
James K. G. Watson
Keyword(s):  
Electronic Transitions ◽  
Spin Interaction ◽  
Rotational Line ◽  
Line Intensities ◽  
Transition Moments ◽  
Linear Molecules

Formulae are given for the intensities of rotational lines in 3Σ–1Σ electronic transitions of linear molecules, allowing for the effects of spin–spin interaction. For [Formula: see text] transitions an error in the relative phases of the two transition moments in the work of Schlapp (1932) is corrected. Recent observations on SO and HCP support this change in phases.

Rotational line strengths in 3Δ–3Σ electronic transitions. The Herzberg III system of molecular oxygen

1986 ◽  
Vol 64 (1) ◽  
pp. 36-44 ◽  
Author(s):  
C. M. L. Kerr ◽  
J. K. G. Watson
Keyword(s):  
Molecular Oxygen ◽  
Satisfactory Agreement ◽  
Electronic Transitions ◽  
Rotational Line ◽  
Spin Orbit ◽  
First Order ◽  
Order Relations ◽  
Transition Moments ◽  
Wave Numbers ◽  
Line Strengths

Electronic transitions of the type 3Δ–3Σ are forbidden in the absence of spin–orbit or orbit–rotation coupling, but spin–orbit perturbations produce three transition moments, two perpendicular (Y1 and Y2) and one parallel (Z1) while low-order orbit–rotation couplings introduce three further perpendicular transition moments (X1, X2, and X3). Formulas are presented for the rotational line strengths in a 3Δ(a)–3Σ(int) transition in terms of these parameters and are applied to recent data of Coquart and Ramsay for the Herzberg III system [Formula: see text] of molecular oxygen. It is shown that all six parameters are significant, and that there are noticeable departures from the first-order relations Y1 = Y2, Z1 = 0, X1 = X2 = X3. The observation of orbit–rotation intensity effects led to the first identification of lines of the Ω′ = 3 subbands of the 4–0 to 7–0 bands of the Herzberg III system, which are forbidden for the spin–orbit mechanism. The wave numbers of these lines are in satisfactory agreement with the analysis of the A′3Δu → a1Δg emission by Slanger and Huestis.

ANOMALOUS ROTATIONAL LINE INTENSITIES IN ELECTRONIC TRANSITIONS OF POLYATOMIC MOLECULES: AXIS-SWITCHING

1965 ◽  
Vol 43 (2) ◽  
pp. 298-320 ◽  
Author(s):  
J. T. Hougen ◽  
J. K. G. Watson
Keyword(s):  
Electronic State ◽  
Electronic Transition ◽  
Electronic States ◽  
Polyatomic Molecules ◽  
Electronic Transitions ◽  
Rotational Line ◽  
Line Intensities ◽  
Fixed Axis ◽  
Axis Switching ◽  
Equilibrium Geometries

It is convenient when performing calculations on a vibrating and rotating molecule to define an axis system which is somehow fixed to the molecule. The orientation of the usual molecule-fixed axis system, however, depends not only upon the instantaneous positions of the nuclei, but also upon the equilibrium positions from which the nuclei are regarded as being displaced. Thus, when a molecule of low enough symmetry undergoes an electronic transition accompanied by a change in geometry, it will, in general, be necessary to consider two molecule-fixed axis systems, corresponding to the two different electronic states. This change in axis system from one electronic state to another will be called axis-switching. The two axis systems can be related to each other by the 3 × 3 rotation matrix which brings them into coincidence. The elements of this matrix are functions of the equilibrium geometries of the two electronic states as well as of the instantaneous positions of the atoms in the molecule. Axis-switching leads to departures from the usual expressions for the intensities of rotational lines, the effects of which are most noticeable in near-symmetric tops. The forbidden subbands occurring in the 2 400 Å system of acetylene can be satisfactorily explained by axis-switching. Axis-switching effects may also be present in the spectra of HCN, HSiCl, and HSiBr.

ROTATIONAL AND VIBRATIONAL INTENSITY DISTRIBUTION OF THE FIRST NEGATIVE BANDS IN SUNLIT AURORAL RAYS

1960 ◽  
Vol 38 (3) ◽  
pp. 458-476 ◽  
Author(s):  
A. Vallance Jones ◽  
D. M. Hunten
Keyword(s):  
Solar Radiation ◽  
Intensity Distribution ◽  
Thermal Equilibrium ◽  
Degrees Of Freedom ◽  
Rotational Temperature ◽  
Dissociative Recombination ◽  
Rotational Line ◽  
Kinetic Temperature ◽  
Excitation Process ◽  
Line Intensities

Spectra of sunlit auroral rays were obtained from Saskatoon during the auroras of September 3/4 and 4/5, 1958. The resolution of these spectra was sufficiently high to enable measurements to be made of the relative intensities of the lines of the 0–0 first negative [Formula: see text] band as well as the relative intensities of bands of the Δυ = −1 sequence of this system. An analysis of the rotational line intensities shows they are consistent with an excitation process in which [Formula: see text] ions in thermal equilibrium with the atmosphere at 2200 °K fluoresce under the influence of solar radiation. The vibrational intensity distribution also is consistent with a fluorescent excitation from a state of thermal equilibrium at about 2050 °K. It is shown that the results are not consistent with a fluorescent excitation process in which the rotational and vibrational degrees of freedom of the [Formula: see text] ions come into radiative equilibrium with the solar radiation. Earlier conclusions that radiative equilibrium did hold for vibration are shown to be in error as a result of the high rotational temperature and the low dispersion used. It is concluded that the destruction of [Formula: see text] ions as a result of dissociative recombination proceeds sufficiently fast to prevent any significant approach to radiative equilibrium. This investigation provides a strong indication that the kinetic temperature of a sunlit auroral ray (perhaps in the 400–500 km region) is in the neighborhood of 2000 °K. This may be somewhat higher than the temperature of the normal atmosphere at this height.

The a4Σ−–X2Π Electronic Transition of SiF

1973 ◽  
Vol 51 (6) ◽  
pp. 634-643 ◽  
Author(s):  
R. W. Martin ◽  
A. J. Merer
Keyword(s):  
Electronic Transition ◽  
Energy Levels ◽  
High Dispersion ◽  
Rotational Line ◽  
Molecular Constants ◽  
Transition Moments

The a4Σ−–X2Π transition of SiF at 3360 Å has been reinvestigated at high dispersion. Our new rotational line assignments show that the energy levels of the 4Σ state, which is very close to case (b) coupling, can be fitted with one rho-type doubling parameter (γ) rather than the two proposed by Hougen to account for Verma's previous results. The relative intensities of the branches have been interpreted in terms of two transition moments, whose ratio shows that the intensity of the a–X system comes mainly from the so far uncharacterized σπ22Σ+–X2Π transition. 'Equilibrium' molecular constants for the a4Σ− state have been derived from analysis of the overlapping sequence bands.

Rotational line strengths in 3Σ+–3Σ− electronic transitions. The β3Σu+ – X3Σg− and A3Σu+ – X3Σg− systems of molecular oxygen

1990 ◽  
Vol 68 (2) ◽  
pp. 231-237 ◽  
Author(s):  
B. R. Lewis ◽  
S. T. Gibson
Keyword(s):  
Molecular Oxygen ◽  
The Other ◽  
Orbit Coupling ◽  
Electronic Transitions ◽  
Rotational Line ◽  
Spin Orbit Coupling ◽  
Spin Orbit ◽  
Other Hand ◽  
Line Strengths

Rotational line strengths are given for 3Σ+(int) – 3Σ−(int) transitions arising from spin–orbit coupling. Observed branch intensities for the forbidden β3Σu+ – X3Σg− transition of O2 may be explained by assuming spin–orbit mixing of β3Σu+ with the B3Σu− and E3Σu− states. On the other hand, observed branch intensities for the Herzberg I A3Σu+ – X3Σg− transition of O2 may be explained only by assuming mixing with 3Σ and 3Π states. In neither case do earlier formulae, derived assuming a single 3Π perturber, apply.

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