--%>

Reducible Representations

The number of times each irreducible representation occurs in a reducible representation can be calculated.

Consider the C2point group as described or Appendix C. you can see that (1) sum of the squares of the entries for each symmetry species is equal to 4, the number of operations, of the group; (2) the sum of the term-by-term products over all the operations for any two different symmetry species is zero. This example illustrates a general feature: the rows of point group tables' act as the components of orthogonal vectors do.

The vector-like property can be expressed mathematically. Let I refer to one row of the character table and j to another row. Let R represent any column of a character table. Thus R is a symmetry operation of any of the classes of symmetry operations. Let nR be the number of operations in the class. (This number is equal to the values in the first row of the character table.) You can verify for any of the character table of appendix C that

Σall classes nR
651_Reducible Representation.png i(R) 651_Reducible Representation.png j(R) = {g   i = j} {0   i ≠ j} 

Where r is the number of symmetry operations in the group. The number g is known as the order of the group.

Example: verify that the rows, which give the characters of the different symmetry species, of the C3v character table of Appendix C, obey the relations.

Solution: the number of symmetry operations in the group, i.e. the order of the group, is obtained from the headings of the character table. Thus we obtain the value of g by adding 1 for the Esymmetry element, for the C3 element, and 3 for the σv element, giving a total of 6.

First we test the i = j relation. We have

For A1: 1(1)(1) + 2(1)(1) + 3(-1)(-1) = 1 + 2 + 3 = 6

For A2: 1(1)(1) + 2(1)(1) + 3(-1)(-1) = 1 + 2 + 3 = 6

For E: 1(2)(2) + 2(-1)(-1) + 3(0)(0) = 4 + 2 + 0 = 6

In a similar way we can test the various i ≠ j possibilities. We have

For A1 and A2: 1(1)(1) + 2(1) (1) + 3(1)(-1) = 1 + 2 - 3 = 0

For A1 and E: 1(1)(2) + 2(1)(-1) + 3(1)(0) = 2 - 2 + 0 = 0

For A2 and E: 1(1)(2) + 2(1)(-1) + 3(-1)(0) = 2 - 2 + 0 = 0

The similarity of the characters of the various symmetry species to orthogonal vectors will lead us to the very useful relation. This equation enables us to calculate, for example, the number of molecular orbitals or the number of molecular vibrations that have the symmetry of the various symmetry species for the point group to which  the molecule belongs. You might want to skip ahead to and become familiar with its use, rather than work through the development of this expression.

The idea that the characters ( 651_Reducible Representation.png R) of any reducible representation are made up of the characters of some of the irreducible representation can be expressed by

651_Reducible Representation.png (R) = Σi aj 651_Reducible Representation.png i(R), where for the class containing the Rth symmetry operation, 651_Reducible Representation.png (R) represents the character for a reducible representation and 651_Reducible Representation.png (R) represents the character for the jth irreducible representation, that in the jth row of the character table, occurs in the irreducible representation, or each row of the character table, occurs in a reducible representation. We focus on the jth row, and we attempt to find the value of ai. First we multiply both sides of equation by nR 651_Reducible Representation.png i(R), and then we sum over all classes of symmetry operations. We obtain

Σall classes nR 651_Reducible Representation.png i(R) 651_Reducible Representation.png j(R) = Σall classes [nR 651_Reducible Representation.png i(R) Σaj 651_Reducible Representation.png j(R)]

According to the right side will give zero contributions except when j = i. then the value of the right side is aj times g, where is the order of the group. Thus

Σall classes nR 651_Reducible Representation.png i(R) 651_Reducible Representation.png j(R) = ai g

From above equation we write the important and useful relation

a= 1/g Σall classes nR 651_Reducible Representation.png i(R) 651_Reducible Representation.png j(R)

   Related Questions in Chemistry

  • Q : Mcq Give me answer of this question.

    Give me answer of this question. The normality of 10% (weight/volume) acetic acid is: (a)1 N (b)10 N (c)1.7 N (d) 0.83 N

  • Q : Unit of molality Select the right

    Select the right answer of the question. The unit of molality is: (a) Mole per litre (b) Mole per kilogram (c) Per mole per litre (d) Mole litre

  • Q : Extensive property Choose the right

    Choose the right answer from following. Which one of the following is an extensive property: (a) Molar volume (b) Molarity (c) Number of moles (d) Mole fraction

  • Q : Moles of chloride ion Select the right

    Select the right answer of the question. A solution of CaCl2 is 0.5 mol litre , then the moles of chloride ion in 500ml will be : (a) 0.25 (b) 0.50 (c) 0.75 (d)1.00

  • Q : Molality of a glucose solution What

    What will be the molality of a solution containing 18g of glucose (having mol. wt. = 180) dissolved in 500g of water: (i) 1m  (ii) 0.5m  (iii) 0.2m  (iv) 2m

  • Q : Explain solid in liquid solutions. The

    The French chemist Francois Marie Raoult (1886) carried out a series of experiments to study the vapour pressure of a number of binary solutions. On the basis of the results of the experiments, he proposed a generalization called Raoult's law which states that, <

  • Q : What is cannizaro reaction? Explain

    Aldehydes which do not have  -hydrogen atom, such as formaldehyte and benzaldehyte, when heated with concentrated (50%)alkali solutio

  • Q : Vapour pressure of methanol in water

    Give me answer of this question. An aqueous solution of methanol in water has vapour pressure: (a) Equal to that of water (b) Equal to that of methanol (c) More than that of water (d) Less than that of water

  • Q : Basicity order order of decreasing

    order of decreasing basicity of urea and its substituents

  • Q : Molecular Structure type The ionic

    The ionic radii of Rb+ and I- respectively are 1.46 Å and 2.16Å. The very most probable type of structure exhibited by it is: (a) CsCl type  (b) ZnS type  (c) Nacl type  (d) CaF2 type

    Discover Q & A

    Leading Solution Library
    Avail More Than 1447158 Solved problems, classrooms assignments, textbook's solutions, for quick Downloads
    No hassle, Instant Access
    Start Discovering

    18,76,764

    1937405
    Asked

    3,689

    Active Tutors

    1447158

    Questions
    Answered

    Start Excelling in your courses, Ask an Expert and get answers for your homework and assignments!!

    Submit Assignment

    ©TutorsGlobe All rights reserved 2022-2023.