GROUP THEORY
CONSTRUCTING CHARACTER TABLE IS FOLLOWED BY 4 STEPS through orthogonality rule
STEP 1 : FIND THE NUMBER OF IRRs
Number of IRs = Number of classes.- In C3v
there is 3 classes so Г1,Г2 Г3
STEP 2: FIND OUT THE DIMENSIONS
Sum of the squares of the dimensions of IRRs = Order of the Group
We have to identify a set of 3 positive integers (I1 I2 I3 dimensions of IRRs) which satisfy this condition
The only value of I which satisfy this condition are 1,1,2 so that I12 = I22
SO 3 IRRs of C3v ,two are 1-D and one is 2-D
STEP 3 : FIND character of two 1-D IRRs
In every point group is 1-D IRR who characters are equal to 1 .this IRRs is called totally symmetric IRR
Thus we have
Which satisfy the rule sum of the square of the characters of all operations in any IRR is equal to the order of the group
FIND characters of another 1-D IRRs Conditions
All the characters of this IRRs equal to +1 or -1
Also IRR must be Orthogonal to Г1
Г1 has six +1 as characters of the sym operations 1 for E ; 2 (1) for C3 ; 3 (1) for σv
The characters of Г2 is Orthogonal to Г1 so it has three +1 and three -1
For E in 1-D is +1 ; for 2 C3 in 1-D is +1 ; FOR 3 σV is -1
2. C3v SYMMENTRY OPERATIONS NH3
C3v Point group contains symmentry elements of
ORDER of the group h =6
• classes of the group = 3
3. CONSTRUCTING CHARACTER TABLE IS FOLLOWED
BY 4 STEPS through
orthogonality rule
STEP 1 : FIND THE NUMBER OF IRRs
Number of IRs = Number of classes.- In C3v
there is 3 classes so Г1,Г2 Г3
STEP 2: FIND OUT THE DIMENSIONS
Sum of the squares of the dimensions of IRRs = Order of the Group
We have to identify a set of 3 positive integers (I1 I2 I3 dimensions of IRRs) which
satisfy this condition
4. The only value of Iwhich satisfy this condition are 1,1,2 so that I1
2 = I2
2
SO 3 IRRs of C3v ,two are 1-D and one is 2-D
STEP 3 : FIND character of two 1-D IRRs
In every point group is 1-D IRR who characters are equal to 1 .this IRRs is called
totally symmetric IRR
Thus we have
Which satisfy the rule sum of the
square of the characters of all
operations in any IRR is equal to the
order of the group
5. Which satisfy the rule sum of the square of the
characters of all operations in any IRR is equal to
the order of the group
Here 2, 3 are number of elements in the two classes of C3 and σV operations
6. FIND characters of another 1-D IRRs
• Conditions
• All the characters of this IRRs equal to +1 or -1
• Also IRR must be Orthogonal to Г1
Г1 has six +1 as characters of the sym operations 1 for E ; 2 (1) for C3 ; 3 (1) for σv
The characters of Г2 is Orthogonal to Г1 so it has three +1 and three -1
For E in 1-D is +1 ; for 2 C3 in 1-D is +1 ; FOR 3 σV is -1
7.
8. STEP 4 : FIND character of two 2-D IRR
LETS Consider like this
Values of x and y can be determinedby taking the crossproducts of Г1Г3 and Г2Г3
