Homework 8B - IR and Raman Calculations

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Name: ______________________________

Section: _____________________________

Student ID#:__________________________

This homework will use the ab initio site by Perri at Sonoma State U. Follow instructions on Homework 6B for an introduction and how to create an account.

To start the calculations

click here: https://chemcompute.org
Click on GAMESS at the top or in the center of the home menu.

Using GAMESS to Calculate the vibrational frequencies of a molecule

The biggest power of computation is the ability to predict or match experiment and thus provide the theoretical underpinnings of an observation. For this calculation, we're going to calculate relevant spectral data.

In the Chemcompute interface, click the button IR to calculate the IR frequency or Raman to calculate the Raman frequency (note the need to use RHF for Raman calculations).

Calculate an IR spectra (is outputted in the calculation panel when you click the IR button) and frequency for HCl, HI, HF, and HBr. Plot the calculated frequencies as a function of molecular weight (or in order of molecular weight) of the molecules HCl, HI, HF, and HBr. Do you notice any trends?

Calculate the Raman spectra for HCl, HI, HF, and HBr. Compare the frequencies with those of the IR spectra.

Submit for Credit:

Molecule	IR frequency (frequencies) of vibrations (cm\(^{-1}\))	Raman frequency (frequencies) of vibrations (cm\(^{-1}\) )
HF
HCl
HBr
HI

Submit the above table filled out for the frequency of each molecule (do not copy from others)

Plot up the IR frequency vs molecule size
Compare the trend.
Provide the IR plot presented in the calculation
Provide an Ansatz: Why don't these spectra look like the vibrations that we saw in class?