Vibrations of CH4: Finding A1 Coordinates

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In summary, the conversation discusses finding the normal vibration coordinate of the A1 representation in terms of the coordinates x, y, and z of each atom in the molecule. It is suggested to use quantum mechanical software for easy calculation, and a recommended book is mentioned. The conversation also mentions the normal modes for CH4 and the need to find the normal mode coordinate Q in terms of the coordinates of the hydrogen atoms. The concept of symmetry and basis representations is also briefly discussed. The conversation ends with the offer to continue the discussion through email and MSN.
  • #1
physicist888
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somone could help me to know how to find the normal vibration coordinate of the A1 representation in terms of the coordinates x,y and z of each atomes ( given: we take the carbone atome as a center of the x,y and z axis ).
 
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  • #2
its really simple if u use some quantum mechanical software like Gaussian, Molpro, etc...but i think its not very easy to computer using hand...If u want to know pls. refer this book..
Molecular Vibrations by Wilson, Decius and Cross..this is a good book for normal mode analysis...
PS: Nowadays no one using their brain to calculate by such coordinates...Just read and understand the theory..and use computational software...its easy...For e.g., CH4 has 5*3-6=9 Normal modes.
 
  • #3
i know that it has 9 normal modes. I've write the normal mode representation in terms of the basis representations, and I've found it equal to A1 + E + T1 + 3T2 , that's mean that there's one mode of symetry A1, and to solve my exercise i should find the normal mode coordinate Q in terms of x,y and z as I've asked before.
the mode of symetry A1 is the stretching out of all the CH . I've calcule the projections , and I've found a result. i don't know if its right or not. and i need to be sure about my answer. i hope you could give me a hand with that.
 
  • #4
hi

Hi I am not very familiar.I just started working with such things...so thought of helping u with my low level of knowledge:rolleyes:...first of all i don't understand by basis representations...But interested to learn from u..how u calculated it...if u have some time..pls reply me...
In ur case..for CH4 (Methane)..i.e., it has Td group. With normal modes A1+A2+E2+3T1+3T2. Again i don't know whether its correct or not!just check it...btw now its holydays..but if this is not so urgent...we can or i can try to make some calculation..off course with softwares:smile:...let u know...
Rajini
 
  • #5
man, there're now E2 in the group Td. I've did the calculation and I am sure about it.
the normal representation = A1 + E + T1 + 3T2 .
ive calcule the normal mode Q in terms of x1,y1,z1, x2,y2... which are the coordinates of the hydrogen atoms. but I am not sure about it. i just want to be sure, and i don't have a lot of time for that. so if you could give me a hand, really ill appreciate that.
and about teaching you about the calculation, no prob i will.
 
  • #6
hi..can u tell me in brief...what does A1, A2, symmetry means...does it same as Ag, Au..today i will try to find out normal modes for ur CH4..
 
  • #7
hey..im always waiting your results...hope youll reply me soon
 
  • #8
normal coordinates:
1 2 3
A' A" A'
Frequencies -- 1310.4290 1310.4755 1310.7241
Red. masses -- 1.1791 1.1791 1.1790
Frc consts -- 1.1930 1.1930 1.1934
IR Inten -- 11.9592 11.9658 11.9521
Atom AN X Y Z X Y Z X Y Z
1 6 0.12 -0.01 -0.00 0.00 -0.00 0.12 0.01 0.12 0.00
2 1 -0.60 0.00 0.00 -0.00 -0.00 -0.60 -0.05 0.09 -0.00
3 1 0.03 -0.17 0.00 0.00 0.00 -0.60 -0.23 -0.54 -0.00
4 1 -0.45 0.17 -0.25 -0.27 -0.19 -0.14 0.06 -0.51 -0.21
5 1 -0.45 0.17 0.25 0.27 0.19 -0.14 0.06 -0.51 0.21
4 5 6
A" A' A'
Frequencies -- 1531.2293 1531.2985 3025.1364
Red. masses -- 1.0078 1.0078 1.0078
Frc consts -- 1.3922 1.3924 5.4341
IR Inten -- 0.0000 0.0000 0.0001
Atom AN X Y Z X Y Z X Y Z
1 6 -0.00 -0.00 0.00 0.00 -0.00 -0.00 0.00 0.00 -0.00
2 1 0.00 -0.00 0.50 0.50 -0.01 -0.00 0.01 0.50 -0.00
3 1 0.00 0.00 -0.50 0.17 0.47 0.00 0.47 -0.17 -0.00
4 1 -0.28 0.41 -0.00 -0.34 -0.23 -0.29 -0.24 -0.16 0.41
5 1 0.28 -0.41 -0.00 -0.34 -0.23 0.29 -0.24 -0.16 -0.41
7 8 9
A" A' A'
Frequencies -- 3146.3090 3146.3337 3146.8136
Red. masses -- 1.1016 1.1016 1.1016
Frc consts -- 6.4249 6.4249 6.4271
IR Inten -- 20.9966 20.9909 20.9555
Atom AN X Y Z X Y Z X Y Z
1 6 0.00 0.00 0.09 0.09 0.00 -0.00 0.00 -0.09 0.00
2 1 0.00 -0.00 0.02 0.02 -0.03 -0.00 0.01 0.86 0.00
3 1 -0.00 0.00 0.02 -0.75 0.29 -0.00 -0.30 0.09 0.00
4 1 0.34 0.23 -0.57 -0.18 -0.14 0.35 0.13 0.07 -0.23
5 1 -0.34 -0.23 -0.57 -0.18 -0.14 -0.35 0.13 0.07 0.23
 
  • #9
the above are the normal coordinates...total 9. first 3 are A', A'' and A' and their freq. are respectively (1310.429, etc)...the coordinates for A' is 0.12 -0.01 and -0.00. Pls. try to understand it...if u want a clear file..then send me ur email...for 5 atoms with 5 diff. corredinates..
have fun
 
  • #10
actualy its hard to understand it like this. here you are my email, and I am connected on msn at the moment, so maybe be we could have a conversation about that. land__life@hotmail.com
 
  • #11
is that what u r looking for!
 

1. What are the A1 coordinates in the vibrations of CH4?

The A1 coordinates in the vibrations of CH4 refer to the modes of vibration where all the atoms in the molecule move in the same direction. These modes are also known as symmetric stretching modes.

2. How many A1 coordinates are there in the vibrations of CH4?

There are a total of 3 A1 coordinates in the vibrations of CH4. This is because CH4 is a tetrahedral molecule with 4 atoms, and the A1 modes correspond to the symmetric stretching of each individual bond.

3. What is the significance of A1 coordinates in the vibrations of CH4?

A1 coordinates play an important role in determining the symmetry and stability of the CH4 molecule. The presence of these modes ensures that the molecule remains symmetrical, and any deviation can result in instability and potential chemical reactions.

4. How can A1 coordinates be experimentally determined in the vibrations of CH4?

A1 coordinates can be experimentally determined through techniques such as infrared spectroscopy or Raman spectroscopy. These techniques involve shining infrared or laser light on the molecule and analyzing the resulting vibrations to determine the frequencies and corresponding A1 coordinates.

5. What is the relationship between A1 coordinates and the potential energy of CH4?

The A1 coordinates in the vibrations of CH4 correspond to the potential energy of the molecule. As the molecule vibrates in these modes, the potential energy increases and decreases accordingly. Understanding the A1 coordinates can help predict the behavior of CH4 in different chemical reactions and environments.

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