Why 3n 6

In a similar manner we can write down the reducible representation for all three rotations and all the vibrations. The representation for ALL the degrees of freedom for the molecule 3N can be written as. Make a note of this - it will come up later! Although the set of characters 9 -1 3 1 is a valid member of the C 2v group it is not particularly useful when discussing molecular properties.

What is really required is the language of the shorthand symmetry species Mulliken symbols, A 1 , B 1 etc. From the information covered above it can be easily shown by inspection that:. The good news is that for other more complex molecules we do not have to perform this task by inspection because:.

Step 1. Take the character table for the molecule and add a row at the bottom. For C 2v we have already shown that these are the characters corresponding to A 1 , B 1 and B 2. Step 2. This is where you realize how useful a real molecular model set is.

To do this you will also need to know where the symmetry elements are and how the symmetry operations affect the molecule. The character table also has all the symmetry operations listed by class along the top row. Thus for water 3 atoms under E there are 3 unmoved atoms, but for C 2 both H's move but since the O atom sits on the C 2 axis it does not change its location and so we record 1 under the C 2 column.

The new set of numbers generated in step 2 3 1 3 1 is also a reducible representation in C 2v and obeys the rules of the group. Step 3. In this step we simply multiply together the characters that have been generated in steps 1 and 2. Its that simple. Studying in Grade 6th to 12th? Registration done! Sit and relax as our customer representative will contact you within 1 business day Continue.

Forum Physical Chemistry vibrational-modes-of-linear-and-non-linear. ArunKumarIL, 8 years ago. Enter email id Enter mobile number. Cancel Notify me. Other Related Questions on Physical Chemistry. View all Questions ». Improve this question. And how many degrees of freedom does each atom have? Add a comment. Active Oldest Votes. Improve this answer. Sign up or log in Sign up using Google.

Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. All I can "understand" that he is trying to determine the degrees of freedom in a way I don't understand and I don't even know why he's trying this way. I basically answered to the topic and explained how to get to the 3N-6 in one correct way. Hopefully OP clarifies. Show 3 more comments. Sign up or log in Sign up using Google.

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