CO2 vibration modes

[winpoj]

When reading a text on climate change I encountered a description of 4 vibration modes of a CO2 molecule: symmetric stretch, asymmetric stretch, vertical bend and horizontal bend. Earlier I also read the terms "in-plane bending" and out-of-plane bending. Could anyone please tell me what the relation is between these? For example, is "vertical bend" a synonym for "in-plane bending"?

[Cumaean]

They're basically the same: whatever you call them, you have to have two bending modes of vibration in planes at right angles to each other. Any other bending vibration can then be described as some combination of the two, and any vibration at all, no matter how complicated, can be described as a combination of the four vibrational modes.

[winpoj]

Thanks for help.

[fo3nix]

Imagine the CO2 molecule -- a carbon atom in between two oxygen molecules, all 3 on a flat line.

symmetric stretch is where both O atoms try to pull outwards, parallel to the line.

asymmetric stretch is where the same happens but the C atom moves in one direction too.

the bending is where the O atoms try and go upwards, purpendicular to the line they're all on, and the C atom tries to go the other way (a bit of a boomerang shape).

[winpoj]

Thank you, fo3nix. Stretching is now crystal clear to me. As for bending - I do understand it in principle. However, my confusion stemms from the fact that, in some sources, I find it categorized into vertical bend and horizontal bend and in some other sources into out-of-plane bending and in-plane bending.