# How to Calculate Excited Molecules in O2 Gas Using Spectroscopy | Mark's Guide

• sciphys1
If you are exciting a gas in equilibrium with another gas, what is the mole fraction of the other gas? If you are exciting a gas in phase change, what is the temperature of the phase change?

#### sciphys1

Hi All,

Lets say I know the absorption cross-section of a gaseous species e.g. O2. I have a pulsed laser of a certain energy and of pulse duration, which will hopefully guide me with the number of photons and I focus that laser beam into a stream of O2 gas. Can I calculate the percentage of molecules I will excite?

I have been scratching my head over this problem apart from others (which I will ask later, one at a time!). It will help a lot if you can help with the clarification.

Note: I am learning about spectroscopy but this is not a homework question.

Thank you for your help.

Mark.

sciphys1 said:
I know the absorption cross-section
Einstein coefficient for absorption, okay.
sciphys1 said:
a pulsed laser of a certain energy and of pulse duration
Wavelength and "flux." Okay. Pulse duration.
sciphys1 said:
Can I calculate the percentage of molecules I will excite?
Number excited. (Past tense.) Steady state percentage? Maybe.

sciphys1 said:
Hi All,

Lets say I know the absorption cross-section of a gaseous species e.g. O2. I have a pulsed laser of a certain energy and of pulse duration, which will hopefully guide me with the number of photons and I focus that laser beam into a stream of O2 gas. Can I calculate the percentage of molecules I will excite?

I have been scratching my head over this problem apart from others (which I will ask later, one at a time!). It will help a lot if you can help with the clarification.

Note: I am learning about spectroscopy but this is not a homework question.

Thank you for your help.

Mark.
You need to know a lot of additional information to be able to do this. The absorption cross section is likely the integrated cross section over the entire spectrum. You need to know if the spectrum is diffuse or sharp -- i.e. are you able to excite the entire ensemble of molecules or only a small subset? What is the laser linewidth, compared with the linewidth of the spectrum you are exciting. If the spectrum is sharp, and you know what rovibrational state of oxygen you are exciting, what is the temperature?

## 1. How does spectroscopy work?

Spectroscopy is a scientific technique that involves using instruments, such as spectrometers, to study the interaction between matter and electromagnetic radiation. It works by passing light through a sample and measuring the amount of light absorbed or emitted at different wavelengths. This allows scientists to identify and quantify the molecules present in a sample.

## 2. What is the importance of measuring excited molecules in O2 gas?

O2 gas is a key element in many biological, chemical, and physical processes. By measuring the excited molecules in O2 gas using spectroscopy, scientists can gain a better understanding of these processes and how they are affected by external factors. This information can be used in various fields, such as environmental studies, medical research, and materials science.

## 3. How do you calculate excited molecules in O2 gas using spectroscopy?

The calculation of excited molecules in O2 gas using spectroscopy involves measuring the absorption or emission of light at specific wavelengths and using mathematical formulas to determine the concentration of the molecules present. This can be done using various spectroscopic techniques, such as UV-Vis spectroscopy, infrared spectroscopy, or Raman spectroscopy.

## 4. What are the limitations of using spectroscopy to calculate excited molecules in O2 gas?

Although spectroscopy is a powerful tool for analyzing molecules, it does have some limitations. One of the main limitations is that it cannot distinguish between different types of molecules that have similar absorption or emission spectra. Additionally, external factors such as temperature and pressure can affect the accuracy of the measurements and calculations.

## 5. How can the results of spectroscopy be used in real-world applications?

The results obtained from spectroscopy can be used in various real-world applications, such as air pollution monitoring, medical diagnostics, and materials testing. For example, by measuring the concentration of excited molecules in O2 gas, scientists can determine the level of pollutants in the air or diagnose certain diseases. In materials science, spectroscopy can be used to analyze the composition and structure of different materials, which can help improve their properties and performance.