Talk:Molecular vibration

message: This is a nice pedagogical article. I only don't like "constant rotational motion", because — in contrast to constant translational motion — rotation gives inertial forces (Coriolis and centrifugal) that are not accounted for in this article. So, I would prefer "zero rotational motion" (quantum mechanically phrased:  J = 0 states). Because the original author is obviously very knowledgeable, I don't want to fiddle around with his/her text. Please author, think about changing "constant rotational motion" to "zero rotational motion". --P.wormer 16:29, 28 March 2007 (UTC)
replies: text: Your comments are most welcome. I wanted to avoid using the term constant angular momentum, but I guess that is technically more correct Another way of expressing the main point would be to say that vibrational coordinates are defined with respect to a set of Cartesian axes that move and rotate with the whole molecule. I'll have to think about this later as I'm travelling abroad tomorrow. The Coriolis force comes into play in vibration-rotation spectra and Coriolis coupling constants can be used as additional data in normal coordinate analysis, but this is surely beyond the scope of an article like this? Centrifugal distortion is not really relevant here. Peter Gans, home page Petergans 18:52, 28 March 2007 (UTC)

text: * Constant angular momentum won't do either, unless the constant is zero. I agree that the centrifugal distortion is not important, but it is more a matter of principle. So, why don't you simply say that that the assumption is that there is no overall (external) motion? Or that the associated effects are neglected, which still is a very good approximation. (BTW I answered your earlier remark on my talk page).--P.wormer 20:18, 28 March 2007 (UTC)
thread_title:  Comments 

message: If anyone can verify it, is :es:Vibración molecular Spanish Wikipedia's version of this article? We can add interlanguage links if this is the case. --HappyCamper 01:50, 2 April 2007 (UTC)
thread_title:  Spanish equivalent 

message: I like to make a few discussion points about redundant coordinates. After agreement is reached the endresult may be included in the main article.
* On the  Hc talk page HappyCamper gives a long summary of what is written about redundant coordinates in Ref. 5 of the main article (Petergans' book). This summary relies heavily on point group symmetry. However, a general theory should cover vibrations of molecules without symmetry. This is what I tried to do in my remark above. 
* HC quotes that: A redundant coordinate is, by definition one in which there is no net displacement of the atoms. My definition above (valid for the H-C-C angles in ethene) could be rephrased thus: A  coordinate is redundant when its change causes a simultaneous and equal displacement of all atoms of the molecule. (A redundant coordinate may give an overall translation and/or overall rotation of the molecule). I can reconcile the two definitions when I interpret the external motions either passively (HC and Petergans), or actively (my definition). In the passive interpretation the frame is rotated/translated by a change in a redundant coordinate and the atoms stay fixed in this frame (no net displacement). In the active interpretation the molecule itself is translated/rotated by changing a redundant coordinate. 
* In the case of BF3 redundancy comes from the relation (valid in the planar case): α12+α23+α31=2π. (α12+α23+α31 is an internal coordinate of A'1 symmetry).
* In mathematical terms: a set of coordinates is redundant if (i) they are dependent or (ii) they are not fully within the internal space (this is the case if they do not satisfy the COM or Eckart conditions).
:: The COM and Eckart conditions are satisfied by definition when I talk about molecular vibrations. Moreover there is a strong link with symmetry. Taking the BF3 example, changes in the three angles α12, α23 and α31 are used as a basis for bending vibrations as the projection operator is applied to a symmetrically equivalent set and the three angles are permuted by the 3-fold rotation operation. It is obvious that the angles between lines meeting at a point are related by a linear expression; the use of rocking and wagging coordinates is designed to be a simple way of avoiding the introduction of redundant coordinates.Petergans 12:57, 5 April 2007 (UTC)
thread_title:  Redundant coordinates again. 

message: Thanks for these comments. I won't be able to do anything until I return to Leeds as I don't have my reference books here in Italy. In the meantime, how about this for an opening sentence?
A molecular vibration occurs when atoms in a molecule are in periodic motion relative to a set of axes that move and rotate with the molecule as a whole.
This will allow me to introduce later (adding a sub-section on Cartesian coordinates)the Coriolis effect in terms of a rotating frame of reference, as discussed in the Coriolis effect article.
I would prefer not to get into redundant coordinates. The problem with writing this sort of article is how to give a synoptic view without making unacceptable simplifications or getting into technical fine details. Ethene was chosen because it illustrates well all internal coordinates except out-of-plane; unfortunately it raises the issue of redundant coordinates. On the other hand redundant coordinates can be effectively ignored as the corresponding eigenvalues of GF are zero.Petergans 07:08, 3 April 2007 (UTC)
replies: text: I would replace "move" with "translate uniformly". If uniform translation is not the case, then an external force accelerates the translational motion of the molecule; we don't want that. The same goes for rotation: we don't want an external torque. Hence "rotate uniformly" (constant angular velocity). If you would like to omit Coriolis and centrifugal forces from the article you can say that the molecule (or, if you prefer, its body-fixed axes) do not rotate. In quantum calculations this is a very common assumption (total angular momentum J = 0).--P.wormer 14:33, 3 April 2007 (UTC)

text: It is a pity that you want to avoid redundant coordinates, but you may be right, it is perhaps too technical. And the point that zero eigenvalues will appear is a good one. Although one must modify the usual generalized eigenvalue programs somewhat to account for possible linear dependencies.--P.wormer 14:33, 3 April 2007 (UTC)
replies: text: Maybe it's a good idea to write redundant coordinates. --HappyCamper 04:10, 4 April 2007 (UTC)
thread_title:  Rotation again 

message: Hi everyone, check out these images:
Image:Boron-trifluoride-vibration-3D-balls.png
Image:Boron-trifluoride-vibration-2D.png
Are these good for the article? --HappyCamper 22:53, 5 April 2007 (UTC)
replies: text: * I leave it to Petergans to decide, because I am not very graphically minded and it is his article. What is π ? Out of plane angle?--P.wormer 00:47, 6 April 2007 (UTC)
replies: text: The idea is good. I would prefer to present the Ben with a set of consistent hand-drawn drafts. Putting in diagrams like these raises the issue of vibration coordinates being changes, for example in bond length, rather than properties of the molecule. I'll think about it and come up with some concrete proposals when I get back to Leeds.Petergans 06:51, 6 April 2007 (UTC)
replies: text: I'll ask Ben to see if he can make another image for us. --HappyCamper 18:38, 14 April 2007 (UTC)
thread_title:  Images 

message: This is wrong in principle. "Coordinate with vibrational spectroscopy" would be acceptible. Raman spectroscopy in all its forms cannot be ignored in the context of this article.Petergans 10:39, 12 April 2007 (UTC)
thread_title:  Coordinate with infrared spectroscopy 

message: A reference to a free program has been added to the article. That program uses "mass-weighted coordinates". I have no knowledge of this method. My guess is that they refer to atomic Cartesian coordinates weighted in some way to the mass of the atom, that is, treating each atom as an oscillator. Can anyone help?
Also your opinion as to whether this is a useful reference for this article will be welcome. It looks a bit abstruse to me and may not meet Wikepedia criteria of validation as the program is offered on an "as is" basis.Petergans 15:58, 7 April 2007 (UTC)
replies: text: * See  this section for an explanation of mass-weighted coordinates. Method is straightforward, only point of discussion is the choice of mass: nuclear, atomic, or effective mass? As regards to the link: I don't have problems with this as long is it is not commercial. Validation is a general problem with Wikipedia. Who validates any article? This is a matter of chance. The same goes for free programs. --P.wormer 18:50, 7 April 2007 (UTC)

text: * As I see it, changes in valence coordinates (bond stretch, valence angle bending, etc.) almost always satisfy the six (linear) Eckart conditions. If they do not, we call them redundant (example: 4 H-C-C angles in ethene. Bending all four of them into the same direction shifts the center of mass—violates the translational Eckart conditions). This obeying of Eckart c.'s is a consequence of the fact that most valence coordinates are  independent of the position and the orientation of the molecule (see this article). The GF method is based on linearized valence coordinates (Wilson s-vectors) and  these also satisfy the Eckart conditions (are by the very definition internal coordinates).  If my view is correct (but I don't exclude the possibility of flaws in my view) then the chemistry and physics definitions coincide.--P.wormer 18:21, 10 April 2007 (UTC)

text: *Petergans, you say that Eckart conditions don't come into it. However, you do speak of internal axes, is it not the case that these axes constitute an Eckart frame? (Recall that a displacement vector expressed with respect to an Eckart frame automatically satisfies the 6 Eckart conditions, the first 3 Eckart conditions being the COM conditions). Another question: is a set of linearized internal coordinates (such as they enter the GF method) containing  a redundant coordinate linearly dependent?--P.wormer 22:46, 11 April 2007 (UTC)
thread_title:  Mass-weighted coordinates 

message: On my user page. Comments will be welcomePetergans 18:12, 14 April 2007 (UTC)
replies: text: I put it in /draft. --HappyCamper 18:28, 15 April 2007 (UTC)
replies: text: Yes, I think the Wikipedian is working on doing the image. So, I think it's on the way. I have to run for now, but just glancing through the article, can we add a little note about how to deal with caged compounds? --HappyCamper 14:30, 22 April 2007 (UTC)
thread_title:  New draft 

message: In the section regarding a Newtonian SHM model of vibration the mass for homonuclear diatomic molecules is given as the total molecular mass, while for the heteronuclear case the reduced mass should be used. However, when applying the reduced mass formula to the homonuclear case the mass found is 1/4 that of the total molecular mass, as it should. So I believe there is an error here. Someone more well versed in the topic, or who has access to the source material should confirm. Thanks. <navaburo> --155.246.141.129 (talk) 15:54, 27 June 2008 (UTC)
thread_title:  Newtonian Model Inconsistency 

message: Atom vibration redirects to this article, while Atom vibrations is a separate one. Please check whether these articles should be merged - and if not, whether it would be more sensible to redirect "Atom vibration" to "Atom vibrations". -- 91.48.252.88 (talk) 15:33, 24 November 2011 (UTC)
replies: text: I agree with you on merging Atom vibrations into this article and I've made a merge proposal. I believe that the issue with the duplicate pages has already been fixed. TripleShortOfACycle (talk - contribs) - (she/her/hers) 13:44, 14 January 2021 (UTC)
thread_title:  Possible duplicate article 

message: A new animated diagram was added yesterday by PakpongICCH444 showing the asymmetrical stretching of methylene group of ethylene. It is a very nice diagram but there are two problems.
* It is redundant because it essentially duplicates the second of six diagrams in the next section for the six vibrations of a methylene group.
* It is labelled as a diagram for ethylene. However since ethylene consists of two identical methylene groups bonded to each other, there are actually two asymmetrical stretching modes corresponding to the in-phase and out-of-phase combinations of the asymmetrical stretches of the two groups. It is true that the six modes show movement of only one CH2 group; this is appropriate for a CH2 group attached to a much larger molecule which is approximately stationary.
In view of these problems, is there a reason for keeping the diagram in the article? Dirac66 (talk) 21:29, 5 November 2015 (UTC)
replies: text: I removed it, but if you change your mind, revert me.  A number of students are in the process of adding content to Wikipedia pages but almost everything so far has been fairly redundant or obvious figures.  I guess they learn something from making these drawings, but I have not seen any improvements yet. Part of the problem is that the class is targeting fairly mature Wikipedia articles, where there are few opportunities for novices. Hope springs eternal.--Smokefoot (talk) 23:05, 5 November 2015 (UTC)
thread_title:  Redundant diagram for CH<sub>2</sub> group 

message: In my opinion, formulas as vi=sqr(k/m)*const are best written without the units - a specification that generally causes wrong ideas in the students about the general validity of the equation. Perhaps my students are *** and I do question the approach used.
But if you specify the dimensions of ni and k, do not forget that of m.
151.29.59.56 (talk) 13:56, 26 July 2022 (UTC)
thread_title:  grams 

message: Hash is a term that is commonly used in the world of computer science and cryptography. It refers to a mathematical function that takes an input (or "message") and produces a fixed-size string of characters, which is typically a sequence of numbers and letters. This string is known as the hash value or simply the hash. Pgmcorp (talk) 10:29, 4 March 2024 (UTC)
thread_title:  Hash