Introduction to Electronic Spectroscopy

[EigenState]

Given the importance of spectroscopy to astrophysical investigations, and certain questions and misconceptions that have been posted here at the forum, I have written an article introducing some of the basic principles of spectroscopy in the hope that such concepts would contribute positively to the understanding of, and appreciation for the significance of spectroscopy thereby enhancing the experience of those actively participating in GalaxyZoo.

This is not an introduction to astrophysical applications of spectroscopy.  It is a discussion of why the energy levels of atoms are discrete and thereby lead to discrete spectral features that are highly characteristic of the atomic species, and provides a basis for understanding the internal conditions that must be satisfied for a radiative transition between energy levels to actually occur.

Contents:

I.  Introduction
II.  Basic Concepts in Quantum Mechanics
III.  Electronic Structure of the Hydrogen Atom
   IIIa.  Quantum Numbers
   IIIb.  The Bohr Model
   IIIc.  Fine Structure
   IIId.  Hyperfine Structure
IV.  Spectroscopic Notation and Term Symbols
V.  Radiative Transitions and Selection Rules
VI.  Conclusions
VII.  Acknowledgments
VIII.  References and Notes
IX.  Glossary of Symbols
X.  Numerical Values of the Fundamental Physical Constants
XI.  Appendix:  Supplemental Material

Introduction to Electronic Spectroscopy

The document is a 446KB PDF file that you can download and study at your convenience.  The file has been scanned at Jotti and VirusTotal and shown to be free of malware.  File hashes follow:

MD5:  3dc0cec63a49859723f5dbc94d9fe539
SHA1:  aaecbcdbcc26006fa374fd3471e0fe6e5b424a20

I would like to thank Jay Lowe for making the original manuscript into the PDF file and for hosting the document.

EDIT:  Chapter 2 can be accessed via Introduction to Spectral Line Profiles

[Alice]

I haven't got that far in reading this yet - it's been a tiring day (and we've only just got back to studying!) - but I heartily recommend this, folks! It could be used as a student's text, but it's beautifully tailored to Galaxy Zoo. EigenState has gone to an amazing amount of trouble here. It's pretty high-level stuff, but very worthwhile.

And that's very nice of you to host it, jlowe. 

[NGC3314]

At Eigenstate's suggestion, I'll add to some links I posted on another thread to keep the context going. The wonderful tracing above of how quantum principles produce emission (and absorption) lines gets about to the point where astrophysical conclusions can start. Further detail on how we go from the QM properties of various energy states of ions to astrophysical conclusions can be found
here, and application in the context of star formation measures here (that one needs updating in light of Spitzer and GALEX results, but the principles are there...) You will quickly see that astronomers usually want to start at about the place Eigenstate's discussion left off. As I tell my students, "This is where Einstein A and B values are defined. Sensible astronomers will go look them up from calculations by people who care about getting the details right". (Eventually this will lead us back into why it is so interesting that the spectrum of Hanny's Voorwerp has strong emission from He II and [Ne V], but that is distinctly another thread).

And, so "electronic spectroscopy" is dealt with specifically, here are some lecture supplements on detectors in astronomy and spectroscopy.

[jlowe]

EigenState's paper provided me with an appreciation of how electronic spectroscopy can expand my understanding and appreciation of the universe - I'd like to share my simple view.

One can use electronic spectroscopy to identify the atoms of galactic objects of interest. Comparing those with known atoms, you can calculate the redshift - velocity the object is moving (red - away, blue - toward) with respect to us. The atomic structure(s) of those objects can lead to classifications into groupings - "spectroscopic morphology", which leads to a fundamental understanding of how the universe develops "cosmology"!

Truth be told,  the physics is beyond me, however, not the appreciation and a basic understanding of what it means. I've found that reading the "Intro" and  the discussion and links provided by NGC3314 has added to the excitement I had when I first stumbled onto GalaxyZoo.

jlowe

[EigenState]

Greetings Jay,

Thank you for those kind words although I am not certain that they are deserved.  And thank you yet again for hosting the document.

Rest assured that you have the option to retract your post after suffering through the forthcoming Chapter 2. 

Best regards,
EigenState

[CloudedHills]

I just thought I might note, the link appears to be broken, and every time I've tried it it just says page not found. (Delete this if you like, I just didn't know where else to say this). Hope it's fixed soon, I've only used spectroscopy in a chemistry context and would really like to know how to apply it to astronomy.

[jlowe]

I just thought I might note, the link appears to be broken, and every time I've tried it it just says page not found. (Delete this if you like, I just didn't know where else to say this). Hope it's fixed soon, I've only used spectroscopy in a chemistry context and would really like to know how to apply it to astronomy.

If anyone else is having problems accessing the link,  send me a message and I'll see if I can't fix it.
...jay

[EigenState]

Greetings,

I just tried the link and it worked without any difficulties.

...I've only used spectroscopy in a chemistry context and would really like to know how to apply it to astronomy.

As stated in the initial post to this thread:

This is not an introduction to astrophysical applications of spectroscopy.  It is a discussion of why the energy levels of atoms are discrete and thereby lead to discrete spectral features that are highly characteristic of the atomic species, and provides a basis for understanding the internal conditions that must be satisfied for a radiative transition between energy levels to actually occur.

Best regards,
EigenState

[CloudedHills]

Greetings,

I just tried the link and it worked without any difficulties.

...I've only used spectroscopy in a chemistry context and would really like to know how to apply it to astronomy.

As stated in the initial post to this thread:

This is not an introduction to astrophysical applications of spectroscopy.  It is a discussion of why the energy levels of atoms are discrete and thereby lead to discrete spectral features that are highly characteristic of the atomic species, and provides a basis for understanding the internal conditions that must be satisfied for a radiative transition between energy levels to actually occur.

Best regards,
EigenState

Ok, sorry for not reading. Should be interesting nevertheless.

[Fire_ice]

im unable to open the link:(  it just comes up as a blank white screen when i click on it

[jlowe]

im unable to open the link:(  it just comes up as a blank white screen when i click on it

Greetings,
   I can help if you send me your IP address, it might be blocked by mistake. An indirect way to get you around the problem is to use GOOGLE to access it for you. Click
here to access it.
Regards,
..jay

[Alice]

Rick, if you like, I can post you a copy of this as a PDF file via regular e-mail. I've downloaded it (and I can see everybody's e-mail address, sorry! But don't worry, I keep  ). In fact, I can post anybody a copy.

Jlowe - thanks for all your trouble, I can see you're putting yourself out a lot to help people.

[Fire_ice]

Thanks the redirect worked fine..now i have a bit of 'light' reading to do lol

[jlowe]

Rick, if you like, I....

Alice,
No problem.. If anyone else is having problems, feel free to drop me a note.

Fire-ice:  Enjoy your read 

..jay

[Fire_ice]

I think i may have finally gotten the basics of spectra down.  I was looking at it all wrong before, which is why it was so confusing.  When observing spectra, it seems that you learn more from whats being absorbed than what is being emmitted.  A very narrow view to be sure, but for the time being it makes things a little clearer.  to test what ive learned, i happened to come upon a lone star in my analisis that had a spectra available, and using the charts on this page -
http://skyserver.sdss.org/dr1/en/proj/advanced/spectraltypes/lines.asp
i came to the conclusion that this is most likely an 'm' class star.  i drew this conclusion becuase of the high absorption of sodioum, along with the strong titanium oxide absorbtion throughout the spectra.  It would be great if someone with a better understanding of this could check this for me, so i can see if ive learned anything between yesterday and today:)