Sciencemadness Discussion Board

Boron green emission orbital transitions ?

fluorescence - 16-10-2016 at 09:01

So I wanted to compare the energy differences between the different Boron group elements in their emissions. I know from Hartree Fock and for the very heavy elements also Relativistic effects, that the energy gap between the orbitals change towards higher energies. Still I expect this to be in an either ascending or descending way but not mixed besides side effects like Rel. Eff. which would cause a bigger gap....I think. Doesn't really matter.

So I found....after an exhausting search....because for some reason nobody is able to just sum stuff like this up....so I had to go via Lasers, their emissions and search for the orbitals.... that Ga, In and Tl all have their two characteristic emissions in an electron transition between the:

xP1/2 or xP3/2 to the (x+1)S1/2 Orbitals. And the wavelenght seems to become longer towards Thallium indicating that the energy gap must become smaller.

Now I know that Aluminium doesn't have an emission in the visible spectum which seems logic as Gallium is already at 403 and 417 nm. But for Boron there still is the famous green flame. Not only Trimethylborate but as far as I know Boric Acid will also produce a green flame.

Now I couldn't find anything on this transition. I think the analogous one to the others should be from 3s -> 2p but I can't even find that one and expect it to be much shorter in wavelenght... the question which Orbitals are involved in this green transition. I tried googling all the terms but couldn't find anything about it.

Greetings,
fluorescence.

zed - 24-10-2016 at 12:48

Umm. I remember calculating the wavelength emission, caused by an electron falling from one orbital to another, in a simple Bohr atom.

My instructor at that time, warned that this calculation worked pretty well, in the simplest case only. After that, ya got other factors gummin' up all yer fancy predictions. Like other electrons and stuff.

So......

blogfast25 - 24-10-2016 at 13:35

Quote: Originally posted by fluorescence  

Now I know that Aluminium doesn't have an emission in the visible spectum which seems logic as Gallium is already at 403 and 417 nm. But for Boron there still is the famous green flame. Not only Trimethylborate but as far as I know Boric Acid will also produce a green flame.

Now I couldn't find anything on this transition. I think the analogous one to the others should be from 3s -> 2p but I can't even find that one and expect it to be much shorter in wavelenght... the question which Orbitals are involved in this green transition. I tried googling all the terms but couldn't find anything about it.

Greetings,
fluorescence.



Not sure where you get that from: emission spectrum of Al:

http://astro.u-strasbg.fr/~koppen/discharge/

and NIST data:

http://physics.nist.gov/PhysRefData/Handbook/Tables/aluminum...

Re boron, the strong colour of a trimethyl borate flame suggests we're looking at molecular orbital transitions, not atomic orbital transitions. I could be wrong on that.

phlogiston - 25-10-2016 at 03:46

This paper states that BO2 is the green-light-emitting species (but does not give a reference for that).

My suggestion would be to check the literature on barium-free pyrotechnic green light emitting mixtures. Boron compounds have received quite a bit of attention for use in 'green'-fireworks (green as in 'less of an environmental problem than barium').

This one by Steinhauser et al is also interesting. A quote:
Quote:
Some boric acid esters burn with a green flame, which suggests a possible application of boron compounds in pyrotechnics. Although, their color intensity cannot compete with barium-based formulations, some pyrotechnic compositions with boric acid as the coloring agent have been tested and show a green flame color with good color purity.26 It has been reported that boron, as a fuel, combusts in oxygen to form B2O3, BO2, and BO in the gas phase.27 The main emitting species in this case is boron dioxide BO2.25 In another study, the infrared emission of boron/alkali-metal nitrate formulations has been investigated. The principal products found were alkali-metal metaborates, B2O3(g), BO(g), and B2O2(g).28


[Edited on 25-10-2016 by phlogiston]