The r-centroid concept revisited

2001 ◽  
Vol 79 (2-3) ◽  
pp. 611-622 ◽  
Author(s):  
R W Nicholls ◽  
M Amani ◽  
M Mandelman
Keyword(s):  
Electronic Transition ◽  
Transition Probability ◽  
Space Physics ◽  
Transition Moment ◽  
Internuclear Separation ◽  
Atmospheric Physics ◽  
Electronic Transition Moment ◽  
Intensity Measurements ◽  
Radiative Transitions ◽  
Recent Developments

The r-centroid concept, was proposed the in 1950s to permit factoring of the band strength integral Sυ',υ'' into the product of the Franck–Condon factor qυ',υ'', and of the square of the electronic transition moment Re (r), when taken at the r-centroid value of the internuclear separation, r = [Formula: see text]υ',υ'', which is the most likely value r at which the υ' « υ'' transition will occur. It has been much used since then in the interpretation of intensity measurements on many band systems of importance in astrophysics, atmospheric physics, space physics, and chemical physics to determine the variation of the electronic transition moment with internuclear separation, and thereby to derive band strengths, and other molecular transition probability parameters. It has been somewhat less used in recent years in the study of individual band systems, since the development of powerful computing facilities now allow for exact ab initio numerical studies to be made of individual molecules and their radiative transitions. Nevertheless the r-centroid concept, and some of its recent developments, provide much insight into the general systematics of diatomic molecular band systems and their spectra. This partly tutorial paper reviews the origins, properties, applications, and recent developments of the r-centroid concept. PACS No.: 33.70

PHOTOELECTRIC INTENSITY MEASUREMENTS UPON BANDS OF THE SiN (B2Σ+−X2Σ+) SPECTRUM

1963 ◽  
Vol 41 (2) ◽  
pp. 240-245 ◽  
Author(s):  
Anne E. Stevens ◽  
H. I. S. Ferguson
Keyword(s):  
Electronic Transition ◽  
Trace Amount ◽  
Transition Moment ◽  
Internuclear Separation ◽  
Electronic Transition Moment ◽  
Intensity Measurements ◽  
Condon Factors ◽  
Microwave Excitation ◽  
Franck Condon

The SiN B2Σ+−X2Σ+ (3800–5200 A) spectrum was excited by continuous introduction of SiCl4 in trace amount into the afterglow produced by microwave excitation of nitrogen. Relative intensities of 21 bands were measured photo-electrically and interpreted with the aid of Franck–Condon factors qν′ν″ and r-centroids [Formula: see text] in terms of the variation of the electronic transition moment Re(r) with internuclear separation r. It was found that Re(r) could be represented empirically by Re(r) = const.(1−1.27r + 0.412r2), [Formula: see text].

AN EXPERIMENTAL STUDY OF BAND INTENSITIES IN THE FIRST POSITIVE SYSTEM OF N2: II. THE TRANSITION MOMENT

1954 ◽  
Vol 32 (7) ◽  
pp. 475-479 ◽  
Author(s):  
R. G. Turner ◽  
R. W. Nicholls
Keyword(s):  
Experimental Study ◽  
Electronic Transition ◽  
Transition Probabilities ◽  
Transition Moment ◽  
Positive System ◽  
Internuclear Separation ◽  
Electronic Transition Moment

Experimental band intensities of the first positive system (B3Πg → A3Σu) of nitrogen are used together with theoretical transition probabilities to determine the dependence of the electronic transition moment on the internuclear separation. Over the range 1.17 < r < 1.59 Å of internuclear separation, this dependence may be represented by Re(r) = const. × exp (−3.02 r).

AN EXPERIMENTAL STUDY OF BAND INTENSITIES IN THE FIRST POSITIVE SYSTEM OF N2: I. VIBRATIONAL TRANSITION PROBABILITIES

1954 ◽  
Vol 32 (7) ◽  
pp. 468-474 ◽  
Author(s):  
R. G. Turner ◽  
R. W. Nicholls
Keyword(s):  
Experimental Study ◽  
Electronic Transition ◽  
Transition Probabilities ◽  
Transition Moment ◽  
Positive System ◽  
Vibrational Transition ◽  
Internuclear Separation ◽  
Electronic Transition Moment ◽  
Infrared Spectrometer ◽  
Integrated Intensities

Integrated intensities of 52 bands of the N2 first positive system have been measured using a recording infrared spectrometer. These data have been interpreted as vibrational transition probabilities which were compared with theoretical values calculated under the assumption that the electronic transition moment is independent of internuclear separation. The comparison shows that the assumption is not valid for this electronic transition.

Intensity measurements in emission of 18 Vegard–Kaplan bands of N2

1968 ◽  
Vol 46 (3) ◽  
pp. 221-226 ◽  
Author(s):  
G. Chandraiah ◽  
G. G. Shepherd
Keyword(s):  
Discharge Tube ◽  
Electronic Transition ◽  
Band System ◽  
Internuclear Separation ◽  
Electronic Transition Moment ◽  
Intensity Measurements ◽  
Condon Factors ◽  
Nitrogen Mixture ◽  
Photoelectric Measurements ◽  
Franck Condon

The Vegard–Kaplan band system of nitrogen was excited by running a low-current discharge through a pure xenon–nitrogen mixture contained in a 6-liter spherical bulb of a discharge tube. Photoelectric measurements of the relative intensities of 18 bands (λ 2340–4324 Å) have been made using a 1-m Ebert–Fastie spectrometer. These measured band intensities were used along with Franck–Condon factors qν′ν″ and r centroids [Formula: see text] to study the variation of the electronic transition moment Re(r) with internuclear separation r. It was found that over the measured range from r = 1.23 to 1.43 Å that Re(r) could be represented by[Formula: see text]A "smoothed" set of band strengths [Formula: see text] was determined from this expression for all the observed bands of the Vegard–Kaplan system.

Sign in / Sign up

Export Citation Format

Share Document