Use this tag for questions about spectroscopic methods in practice and in theory, especially where tags for the individual method (such as [tag:nmr] or [tag:ft-ir]) are not available.

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6
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1answer
141 views

How to determine the structure of organic molecules without spectroscopy [duplicate]

I wonder how chemists worked out the structures of organic molecules before spectroscopy (especially NMR) was invented? Surely, we could do functional group tests, but the correct connection of atoms ...
-1
votes
1answer
59 views

Unusual triplet in 13C-NMR

Why is there a triplet at 46.7 ppm in the following spectrum of 2,2,2-tribromoethan-1-ol?
27
votes
3answers
4k views

Can hot food ever emit x-rays or gamma rays?

I was just wondering, if heating food up is the result of increasing the energy of bends and stretches in the bonds of the molecules, is it ever possible for tiny amounts of x-rays and gamma rays be ...
1
vote
0answers
23 views

Is UV-Vis absorption polarization dependent ? Why?

Consider molecule of interest be dissolved in a solvent (and this molecule has absorption in the visible region). We are using a broadband visible light source say tungsten lamp. This light passed ...
0
votes
3answers
31 views

What techniques can determine the concentration of ethyl acetate in a solution containing ethyl acetate, acetic acid, ethanol and water?

I need to monitor the concentration of ethyl acetate in an Fischer esterification reaction. What techniques or spectroscopies can detect the concentration of the compound? And which one do you ...
3
votes
2answers
130 views

What is the correct way to verify a structure's geometry, for example for benzene?

My goal is to compare a calculated bond length with experimental data. Benzene is obviously common enough to expect sufficient experimental data to be available for it on the internet. I have found ...
0
votes
0answers
11 views

How is there 1G term symbol when the max L is 3F for a free ion which has 3d2 electrons

I am very confused as to why there is a G term symbol when the ground state of a free ion = 3F. This is for a 3d2 free ion and I am very confused....I would like to think it might be because when the ...
0
votes
0answers
31 views

Why do ionisations from non-bonding orbitals result in little/no vibrational structure in a photoelectron spectrum?

I understand that ionisations from bonding and antibonding orbitals create vibrational structure from the Franck-Condon principle, resulting in a greater overlap integral between different vibrational ...
4
votes
2answers
86 views

How to convert SPC files to ASCII without original spectroscopy software?

IR and Raman spectroscopy are typically saved in *.SPC files (chemical/x-galactic-spc), which are binary files. Collected data is save to SPC files by default, but can be exported to txt (ASCII) files....
1
vote
0answers
19 views

AAS background correction with Zeeman effect

I've found here the explanation to how Zeeman effect can be used for background correction. I understand everything up to this part: "When light is polarized parallel to the field, both atomic and ...
1
vote
0answers
63 views

19F MAS NMR chemical shift tensor and the crystal structure

$\ce{^{19}F}$ MAS NMR is measured on fluorine-doped $\ce{TiO2}$. $\ce{F}$ is to substitute $\ce{O}$ and the crystal structure is anatase, which has a tetragonal crystal system with a space group $\ce{...
2
votes
0answers
64 views

Is a substance's band gap related to it's flame test colour?

This is really not my field at all, but I am intruiged by the cause of different metals emitting different wavelengths of light. To my knowledge, the more energy needed to "excite" an electron, the ...
1
vote
1answer
29 views

What makes a species “fluorescence quencher”?

I just came across an article where they said that sodium fluoride is not quencher (in the context of fluorescence). Why is NaF not a quencher but NaBr is one?
2
votes
1answer
68 views

basics of NMR (spin-spin splitting)

here's what I wrote from lecture, what i'm confused about is, if two magnetic moment(B0 and the one of red H) have the same direction. wouldn't the magnetic field by red H cancel out the external ...
4
votes
2answers
92 views

Transmission, absorption, and reflection of light

My understanding is: when light hits an object, it can do one of three things: transmit through the object, be absorbed into the object, or reflect from the object. However, I have also learned that ...
3
votes
1answer
42 views

Reasonably complete infrared spectral database with data in CSV form?

I'm currently developing a neural network that analyses IR spectroscopy signatures. I've found a very complete data set at The Spectral Database of Organic Compounds, but data is only available as ...
3
votes
1answer
92 views

Isotropic Fermi Contact Couplings vs. Dipolar Coupling Constant

I need to calculate a Dipolar Coupling Constants for some fancy triplet molecule that has been measured by EPR spectroscopy. My "normal" output from Gaussian gives me the following: Isotropic Fermi ...
-1
votes
1answer
79 views

What would the calibration graph look like if…? Please help [closed]

In my lab, I had to use spectroscopy to determine the concentration of protein in milk whey from buttermilk and understand how absorbance of light is related to concentration (Beer's Law). This was ...
3
votes
1answer
26 views

Changing the spectroscopy type to infrared in GC-MS

I know you can use GC-MS for the analysis of gaseous molecules, but would you be able to instead use an infrared spectroscopy method to analyse gaseous molecules, or does it need to be mass ...
7
votes
2answers
956 views

Why use TMS in NMR spectroscopy

I get the thing that TMS has a large proton number giving a strong spike in NMR spectrum but apart from that is there any other reason why just TMS is used and not any other molecule, can't it be a ...
12
votes
1answer
110 views

Photoionisation microscopy of hydrogen - where are the p orbitals?

In this Physics Review Letters article, which was published in 2013, but I found recently, the authors report photoionisation microscopy images of hydrogen atoms in various electronic states. A. ...
1
vote
0answers
28 views

why the formula of coca cola can not be find using chemistry? [duplicate]

i mean we have SPECTROSCOPY to stablish what molecules make a compound and also we have advanced chemistry so why is SO HARD to find the formula of coca cola ? simply buy a bottle examine it to ...
1
vote
0answers
22 views

IR spectrum of an organometallic compound [closed]

In a solution IR of [CpFe(CO)2]2 (Cp = cyclopentadienyl), 3 peaks are observed. These are: 2006, 1962 and 1794 cm-1. Questions: 1. Why are there 3 peaks (hint: molecular symmetry)? 2. What does each ...
3
votes
0answers
17 views

excitation upon emission from 2 LEDs

I came across a problem: I have 2 LEDs with different emission spectra (blue and green). I have 1 molecule with a known excitation spectrum (channelrhodopsin2 protein). I turn on 1 LED at a time. ...
10
votes
2answers
238 views

Determining structure using ¹H NMR and IR

I have a homework problem where I'm to draw the structure of a compound of molecular formula $\ce{C10H12O2}$ using the following IR data and $^1$H NMR spectrum: IR absorption at 1718 cm$^{-1}$ ...
0
votes
2answers
37 views

What type of analytical chemistry (such as spectroscopy) is suitable for high resolution air analysis

I want to find some type of analytical chemistry method, such as spectroscopy, that is capable of analysis the chemical composition of air. If it can be used for high resolution analysis would be ...
2
votes
1answer
70 views

Coupling constant in 1H NMR with phosphorus

I had a doublet with peaks at 5.6336 and 5.5886 ppm with the machine running at 300 MHz, I got a $J_P$$_H$ of 13.5 Hz is this correct for this molecule ( Ethoxycarbonylmethyl(triphenyl)phosphonium ...
0
votes
0answers
18 views

Is there a published list of adsorption vibrational frequencies of different mocules on different substrates?

Calculating vibrational adsorption frequencies of adsorbed molecules on substrates can be a very difficult task involving solving the vibrational Schrodinger equation. Some published Journals in the ...
1
vote
2answers
71 views

what is the difference between excitation and emission spectroscopy?

I know about absorption spectroscopy but really confused between excitation and emission spectroscopy. If they are different, then how?
1
vote
0answers
20 views

EPR spectrum of a singlet-triplet mixture

Through EPR measurements it is possible to gain information about the spin states of molecules. So a singlet state will give no signal/only noise and a molecule with unpaired electrons will result in ...
0
votes
0answers
15 views

Auger emission probability?

Why is it that lighter atoms are more likely to produce Auger emission and the heavier atoms fluorescence in x-ray spectroscopy? It doesn't make any sense. Lighter atoms should try to resist double ...
2
votes
0answers
27 views

S-N bond IR vibrations

I am working on organosulfur compounds where i have S-N bonding, according to literature it might be having an ir vibration of 1100cm-1, could anyone confirm it with reference. (the complete bonding ...
1
vote
3answers
46 views

How estimate E0-0 of an organic dye?

How can I estimate the $E_{0-0}$ value of an organic dye? I have obtained the UV-vis absorption and fluorescence spectra of this dye in solution. This article talks about (in Table 2 notes) the ...
2
votes
1answer
74 views

How many vibrations are expected for butatriene and cyclobutadiene?

I have butatriene and cyclobutadiene, the formula for finding the number of vibrations expected are Linear: $3N-5$ Nonlinear: $3N-6$ where $N$ is the number of atoms. Both of these molecules are $...
3
votes
0answers
46 views

Why does an asymmetrical stretch require less energy than a symmetrical one?

I learned that the $\ce{N-H}$ bonds in a primary amine make two signals in ~3400 $\mathrm{cm^{-1}}$, the first one for the symmetrical stretching and the second one for the asymmetrical stretching. I ...
2
votes
0answers
37 views

SERS Gold nanoparticles performing poorly in organic solvents?

We have been working with some organic solvents lately and noticed a sharp decrease in surface-enhanced Raman spectroscopy (SERS) performance from our gold nanoparticles deposited in an organic ...
0
votes
0answers
37 views

Assigning IR of [Cu3(btc)2]

I am trying to identify the peaks due to the carboxylate groups in the IR of $\ce{[Cu3(btc)2]}$. I think that the large peaks at $1643.76~\mathrm{cm^{-1}}$ and $1369.19~\mathrm{cm^{-1}}$ are both ...
6
votes
2answers
154 views

How to explain the discrepancy between the calculated absorption wavelength within the particle in the box theory and the observed wavelength?

The experimental observed wavelength for this molecule is 425 nm. We are supposed to estimate this wavelength theoretically using this equation (energy change in a 1D box), where $N$ is the number of ...
4
votes
1answer
200 views

How to identify the number of pi electrons in a conjugated system to calculate the HOMO-LUMO gap with the particle in the box approach?

It's my understanding that for a particle in a 1-D box, the change in energy from the HOMO to LUMO can be approximated with the following equation: $$\Delta E=\frac{h^2 ( N + 1 )}{8 m_\mathrm{e} L^2}$$...
4
votes
1answer
52 views

Proportionality between number of absorbed photons and optical density

I am to show that the number of absorbed photons only is proportional to the optical density at low optical densities. I do not know how to do this, but this reminds me of the linear range of ...
2
votes
0answers
18 views

Effects on Stretching Frequencies in Organometallic Complexes

If you added a negative charge to $\ce{Mo(CO)_6}$ how would this effect the $\ce{CO}$ stretching frequency in an IR spectrum? My thoughts are that it would lower the $\ce{CO}$ stretching frequency ...
3
votes
1answer
89 views

Calculating Raman Intensities from Static Raman Activities

Whenever I want to calculate a Raman spectrum, my quantum chemical programs give me Raman scattering activities. As the common Raman spectrum is dependent on the incident wavelength of the used laser ...
2
votes
0answers
137 views

How calculate spectral overlap integral using spreadsheets?

I need to calculate the spectral overlap integral for the emission spectrum of coumarin 334 and the absorption spectrum for rhodamine, using spreadsheets (MS Excel). Following the theory of ...
1
vote
0answers
50 views

Comparing IR stretching bands in molybdenum complexes

Why would the infrared stretching frequency of $\ce{CO}$ (which is about $2140~\mathrm{cm^{-1}}$ in gaseous form) be $1982~\mathrm{cm^{-1}}$ in $\ce{[Mo(CO)_6]}$ and even lower in $\ce{[Mo(CO)3(η^6$\...
0
votes
0answers
50 views

Assigning Mass Spectrum of $\ce{(NPCl2)3}$

I'm trying to assign the mass spectrum of the heterocyclic compound $\ce{(NPCl2)3}$ The mass spectrum is as follows: My annotations show that I think the molecular ion is the peak at 346.9 m/z and ...
1
vote
0answers
60 views

Infrared Spectroscopy of Hexachlorocyclotriphosphazene

When assigning the IR spectrum of hexachlorocyclotriphosphazene there are two prominent peaks (one due to the nitrogen-phosphorus bond and the other due to the phosphorus-chlorine bond). There is ...
6
votes
2answers
199 views

Peak Wavelength of Emission Spectrum of a Flame vs. Actual Flame Temperature

I am looking at a lab test of two variants of mixed hydrocarbon gas (57.8% $H_2$, 16.9% $N_2$, 12.4% $CH_4$, 1.11% water vapor, and 11.8% "unknown" gases) burning in oxygen which shows a discontinous ...
3
votes
0answers
56 views

What would you recommend to isolate these compounds from cooking oil?

Recycled cooking oil, aka "gutter oil", is a major problem in countries such as China. I am doing some research to see if there's a reliable and quick way to determine if something is gutter oil. I ...
6
votes
1answer
190 views

Interchange of axial and equatorial groups in Me2NPF4

The $\ce{^{31}P}$ NMR spectrum of $\ce{Me2NPF4}$ when recorded at room temperature consists of a quintet with intensities $1:4:6:4:1$. However, at $-100~\mathrm{^\circ C}$, the spectrum is as shown ...
1
vote
1answer
49 views

What is the typical range for the molar absorptivity of paint?

For example, $\ce{TiO2}$ is used a lot as pigments in paint, what is the range of molar absorptivity for that? Would I be able to determine this from this graph: Ideally I could estimate a range ...