ATAR Notes: Forum

VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Chemistry => Topic started by: StringFever on June 07, 2009, 09:34:16 am

Title: Pulsing Lights
Post by: StringFever on June 07, 2009, 09:34:16 am

Hey guys,

Just a brief one - I was revising with my friends a few days ago, and our discussion steered onto the topic of spectroscopic analysis. One of my friends mentioned that he had read somewhere that a particular spectroscopic technique involved the pulsing of light. I haven't really heard of pulsed lights used to spectroscopic techniques. I was reading my notes, and the only conclusion I could come up with was that perhaps it was used in the double beam scanning spectrophotometer (a form of UV-Vis where "apparently" light is chopped/passed alternatively through two cells - a reference cell and the sample cell).

Does anyone know whether that is true? ???

Title: Re: Pulsing Lights
Post by: mystikal on June 07, 2009, 09:51:49 am

reference cell and sample cell are from Infrared Red Specs

AAS is related to pulsed light thingy

Title: Re: Pulsing Lights
Post by: Dark Horse on June 07, 2009, 11:00:09 am

In AAS, light is pulsed from the hollow cathode lamp so that the detector is able to differentiate between absorbed and emitted light (cos remember, while the electrons in atoms absorb the energy from the hollow cathode lamp to become excited, the excited state is unstable, so the electron returns to the ground state, emitting energy, which is of the same wavelength to that absorbed.) :)

Hope that helped!

Title: Re: Pulsing Lights
Post by: StringFever on June 07, 2009, 03:10:03 pm

Thanks Dark House that did :)

I completely forgot that without the pulsing light, the detector would just detect 0% absorbance. :P

Title: Re: Pulsing Lights
Post by: StringFever on June 07, 2009, 05:21:59 pm

Just another quickie - does pulsing light happen in UV-Vis or not?

Title: Re: Pulsing Lights
Post by: mystikal on June 07, 2009, 07:38:59 pm

nope

Title: Re: Pulsing Lights
Post by: StringFever on June 07, 2009, 09:57:45 pm

Quote from: mystikal on June 07, 2009, 07:38:59 pm

nope

Would you mind explaining why - because doesn't it seem logical for it to happen because it follows a similar methodology to AAS and pulsing lights happen in AAS?

Title: Re: Pulsing Lights
Post by: Mao on June 08, 2009, 11:14:47 am

AAS is performed with ambient light, UV vis is performed in completely isolated and dark environment, hence pulsing is not required.

AAS cannot be performed in completely isolated and dark environment because of the flame. But this is not important as atoms can only absorb specific wavelengths.