Difference between revisions of "HCl Vibrational-Rotational Spectroscopy"

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 +
(3/26/20, bes)
 +
 
Adapted from Experiment #38 (Shoemaker, Garland, Nibler, 1989)
 
Adapted from Experiment #38 (Shoemaker, Garland, Nibler, 1989)
  
−
1) Sample preparation
+
See Chapter 8 (Engel), more will be presented in lecture...
 +
 
 +
===Sample Preparation===
 +
:a) Pull the HCl (g) off the headspace of a bottle of concentrated HCl using a 60 mL syringe.
 +
:b) deliver the HCl (g) to the gas-sampling IR cell.
 +
 
 +
===IR Gas-Phase Data Collection===
 +
:a) Collect data using the highest resolution.
 +
:b) average 32 scans (both background and sample)
 +
:c) Save-As...
 +
::(A complete set of data can be found [[Media:HCl.CSV|here]].)
 +
 
 +
===Spectral Analysis===
 +
:a) load IR data into Igor or Excel.
 +
:b) Use the cursor tool to tabulate the H<sup>35</sup>Cl and H<sup>37</sup>Cl data into separate columns,
 +
:c) Assign an ''"m-value"'' to each transition (note the ''''m=0'''' forbidden transition) with the help of the following graphic (click to make bigger).
 +
 
 +
 
 +
:WRONG --> [[File:Screen Shot 2020-03-26 at 8.48.29 AM.png|200px]]
 +
:RIGHT --> [[File:Screen Shot 2020-03-27 at 12.35.55 PM.png|400px]]
 +
 
 +
===Data Analysis===
 +
Okay, so you should now have a table, probably in Excel but if you know how to do it in Igor then great (Igor does not offer any advantages here) with heading like this:
 +
{| border=1
 +
|''m-value''||H<sup>35</sup>Cl||H<sup>37</sup>Cl
 +
|-
 +
| -12 || XXXX  ||YYYY
 +
|-
 +
| -11 || XXXX  ||YYYY
 +
|-
 +
| -10 || XXXX  ||YYYY
 +
|-
 +
| -9 || XXXX  ||YYYY
 +
|-
 +
| ... || ... ||...
 +
|-
 +
| +1 || XXXX  ||YYYY
 +
|-
 +
| +12 || XXXX  ||YYYY
 +
|-
 +
| +13 || XXXX  ||YYYY
 +
|}
 +
 
 +
:a) Make a plot, m-value verses freq (in 1/cm) for H<sup>35</sup>Cl data; this will NOT be a straight line but a polynomial curve.
 +
:b) fit a second order polynomial to this data... ie ''y= ax<sup>2</sup> + bx +c'', and note the values for a, b, and c in your notes (lab notebook preferred).
 +
:c) During our last lab period you were given a Shoemaker, ''et al.'' handout (???) that discussed this lab activity. Eq. 9 was:
 +
 
 +
<div align="center"> ''ṽ = ṽ<sub>o</sub> + (2B<sub>e</sub> - 2 α<sub>e</sub>) m - α<sub>e</sub> m<sup>2</sup>,  which has the form y = c + bx + ax<sup>2</sup>''</div>
 +
''
 +
:::a = α<sub>e</sub>
 +
:::b = 2B<sub>e</sub> - 2 α<sub>e</sub>''
 +
:::so you can solve for B<sub>e</sub> (this is called the rotational constant and has units of 1/cm)...
 +
 
 +
:::and Be = [[File:Screen Shot 2020-03-26 at 9.36.14 AM.png|200px]]
 +
 
 +
:d) Now solve for the radius (r), the average internuclear separation of the H<sup>35</sup>Cl...
 +
:e) repeat above for H<sup>37</sup>Cl.
 +
 
 +
====Reduced mass calculations====
 +
::https://en.wikipedia.org/wiki/Isotopes_of_chlorine
 +
 
 +
::[[Media:Atomic mass abund.pdf|atomic masses in amu]]
 +
 
 +
::Reduced mass, ''μ = (m1*m2)/(m1+m2)''
 +
 
 +
::::<sup>1</sup>H 1.007825 amu (99.9885%)
 +
 
 +
::::<sup>35</sup>Cl 34.968853 amu (75.78%)
 +
 
 +
::::<sup>37</sup>Cl 36.965903 amu (24.22%)
 +
 
 +
::::conversion factor: 1.66054e-27 kg/amu
  
−
2) IR Gas-phase data collection
+
===WebMO/Gaussian Calculation===
 +
WebMo/Gaussian calculation can be done to determine the B<sub>e</sub>, the rotational constant. It is usually required to specify the specific isotope for the atoms. This can be done by editing the input file (the z-matrix) within WebMO.
 +
:- choose "preview", then "generate" when submitting your job...
 +
:- add the text (Iso=35) or (Iso=37) after the Cl in the input file; for completeness add (Iso=1) after the H as well:
 +
[[File:Screen Shot 2021-03-18 at 1.26.16 PM.png|400px]]
 +
[[File:Screen Shot 2021-03-18 at 1.26.43 PM.png|400px]]
  
−
3) Spectrum analysis including analysis of state populations.
+
===REPORTING===
 +
'''''Please send email with the following information:'''''
  
−
4) Determination of B<sub>e</sub> and alpha<sub>e</sub> (Eq, 19)
+
:H<sup>35</sup>Cl data
 +
::''ṽ<sub>0</sub> =
 +
::Be =
 +
::μ (H<sup>35</sup>Cl) =
 +
::r = ''
  
−
5) Solve for "r" the average internuclear separation.
+
:H<sup>37</sup>Cl data
 +
::''ṽ<sub>0</sub> =
 +
::Be =
 +
::μ (H<sup>37</sup>Cl) =
 +
::r =
 +
''

Latest revision as of 18:40, 18 March 2021

(3/26/20, bes)

Adapted from Experiment #38 (Shoemaker, Garland, Nibler, 1989)

See Chapter 8 (Engel), more will be presented in lecture...

Sample Preparation

a) Pull the HCl (g) off the headspace of a bottle of concentrated HCl using a 60 mL syringe.
b) deliver the HCl (g) to the gas-sampling IR cell.

IR Gas-Phase Data Collection

a) Collect data using the highest resolution.
b) average 32 scans (both background and sample)
c) Save-As...
(A complete set of data can be found here.)

Spectral Analysis

a) load IR data into Igor or Excel.
b) Use the cursor tool to tabulate the H35Cl and H37Cl data into separate columns,
c) Assign an "m-value" to each transition (note the 'm=0' forbidden transition) with the help of the following graphic (click to make bigger).


WRONG --> Screen Shot 2020-03-26 at 8.48.29 AM.png
RIGHT --> Screen Shot 2020-03-27 at 12.35.55 PM.png

Data Analysis

Okay, so you should now have a table, probably in Excel but if you know how to do it in Igor then great (Igor does not offer any advantages here) with heading like this:

m-value H35Cl H37Cl
-12 XXXX YYYY
-11 XXXX YYYY
-10 XXXX YYYY
-9 XXXX YYYY
... ... ...
+1 XXXX YYYY
+12 XXXX YYYY
+13 XXXX YYYY
a) Make a plot, m-value verses freq (in 1/cm) for H35Cl data; this will NOT be a straight line but a polynomial curve.
b) fit a second order polynomial to this data... ie y= ax2 + bx +c, and note the values for a, b, and c in your notes (lab notebook preferred).
c) During our last lab period you were given a Shoemaker, et al. handout (???) that discussed this lab activity. Eq. 9 was:
ṽ = ṽo + (2Be - 2 αe) m - αe m2, which has the form y = c + bx + ax2

a = αe
b = 2Be - 2 αe
so you can solve for Be (this is called the rotational constant and has units of 1/cm)...
and Be = Screen Shot 2020-03-26 at 9.36.14 AM.png
d) Now solve for the radius (r), the average internuclear separation of the H35Cl...
e) repeat above for H37Cl.

Reduced mass calculations

https://en.wikipedia.org/wiki/Isotopes_of_chlorine
atomic masses in amu
Reduced mass, μ = (m1*m2)/(m1+m2)
1H 1.007825 amu (99.9885%)
35Cl 34.968853 amu (75.78%)
37Cl 36.965903 amu (24.22%)
conversion factor: 1.66054e-27 kg/amu

WebMO/Gaussian Calculation

WebMo/Gaussian calculation can be done to determine the Be, the rotational constant. It is usually required to specify the specific isotope for the atoms. This can be done by editing the input file (the z-matrix) within WebMO.

- choose "preview", then "generate" when submitting your job...
- add the text (Iso=35) or (Iso=37) after the Cl in the input file; for completeness add (Iso=1) after the H as well:

Screen Shot 2021-03-18 at 1.26.16 PM.png Screen Shot 2021-03-18 at 1.26.43 PM.png

REPORTING

Please send email with the following information:

H35Cl data
ṽ0 =
Be =
μ (H35Cl) =
r =
H37Cl data
ṽ0 =
Be =
μ (H37Cl) =
r =

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