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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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 ...
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51 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 ...
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0answers
60 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 ...
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1answer
22 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?
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1answer
58 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 ...
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2answers
41 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
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1answer
29 views

reasonably complete spectroscopy 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 ...
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1answer
59 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 ...
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1answer
72 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 ...
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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 ...
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2answers
430 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 ...
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1answer
103 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. ...
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27 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 ...
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20 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 ...
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0answers
16 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. ...
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2answers
212 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$^{-1}$ ...
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2answers
35 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
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1answer
51 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 ...
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0answers
14 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 ...
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2answers
52 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?
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0answers
19 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 ...
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0answers
11 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 ...
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0answers
24 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 ...
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1answer
28 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 ...
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1answer
69 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 ...
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0answers
41 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 ...
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32 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 ...
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31 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 ...
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2answers
136 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 ...
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1answer
172 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} ...
4
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1answer
37 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
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0answers
14 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 ...
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44 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 ...
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92 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 ...
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46 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 ...
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0answers
47 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 ...
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49 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 ...
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2answers
167 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 ...
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54 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 ...
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1answer
154 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 ...
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26 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 ...
3
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2answers
366 views

Why is the carbonyl IR frequency for a carboxylic acid lower than that of a ketone whilst an ester is higher than a ketone

The approximate stretching frequencies are as follows: Acid: $1710$, Ketone: $1715$, Ester: $1730$ (all $\mathrm{cm^{-1}}$) This would seem to suggest that the acid decreases the carbonyl bond ...
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2answers
280 views

Why does an acid anhydride have two infra-red stretching frequencies

The carbonyl stretching frequencies for an acid anhydride are approximately $1820\rm~cm^{-1}$ and $1760\rm~cm^{-1}$. These are both higher frequencies than a simple ketone owing to the electron ...
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32 views

spectroscopy as a pharmaceutical career [closed]

Is studying spectroscopy form it's fundamental perspective regarding "group theory" , "molecular schrodinger equation" and theoretical basis for IR & Raman analysis important for pharmacists ...
4
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1answer
88 views

Interpretation of 1H-NMR spectra for Z-ochtodenol

I'm struggling to understand the 1H-NMR data for this compound. I managed to find the compound using the data I had, but at the end I can't assign the peaks properly. My confusions are: ...
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1answer
65 views

Why absorption/transmission spectroscopic data is normalized?

A typical data processing step for acquired absorption/transmission data is normalizing, i.e. stretching the curve such that it is bounded between 0 and 100%. However, the absorption/transmission ...
6
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1answer
159 views

Why can't carbon and nitrogen be detected in ICP-MS and ICP-OES techniques?

Why can't carbon and nitrogen be detected in ICP-MS and ICP-OES techniques? My book says this technique is efficient for detecting multiple elements, with exception of halogens and carbon. I found ...
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1answer
84 views

Hydrogen's confusing purple glow

While reading about hydrogen on Wikipedia, I read that hydrogen has a purple glow in its plasma state. This confused me because although hydrogen is present in its plasma state on the sun, the sun ...
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118 views

Tables/database/literature of specific or optical rotation

I'm looking for a comprehensive reference of experimental specific rotation or optical rotation data. It can be a published literature review, a free web database with API access or one that permits ...
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0answers
24 views

Observe from IR/Raman spectra whether molecule is in a local minimum on PES

I have done a geometry optimization of cis and trans-difluoroethene using RHF/STO-3G in Gaussian03. Although this is a simple method and a small basis set, this should ideally put place the molecule ...