Questions tagged [spectroscopy]

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

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2
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1answer
101 views

XPS/EDS vs FTIR/Raman [closed]

So I have been studying the four methods the past couple of weeks. To my understanding, XPS is a very surface-sensitive technique. It can give information about the composition of the surface but also ...
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0answers
19 views

Raman or FTIR spectroscopy to identify metals?

Metals are opaque, so doesn't most of the light reflect? And does the IR source even cause vibrations in the metal? Same goes for Raman spectroscopy, is it useful for use of metal identification? Is ...
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3answers
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How to simulate a Lorentzian broadened spectrum in MATLAB?

I'm trying to simulate the 2nu2 band of HCN in MATLAB. I generate a stick spectrum from the data I have (taken from the HITRAN database) and then use conv() to ...
6
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0answers
73 views

Solving the Schrödinger equation for a rotating triatomic linear molecule

This source is showing that solving the Schrödinger equation for a triatmoic linear molecule yields the same formula for the rotationaI quantum states $BJ(J+1)$ as for dipoles. For dipoles, the total ...
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1answer
34 views

Reason for same frequency of spectral line in infrared and visible region

I encountered this question while trying to understand the basics of spectroscopy and atomic structure. Which electronic transition in Balmer series of hydrogen atom has same frequency as that of n=6 ...
2
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3answers
131 views

Carbon in Glass - XPS Analysis

I was reading a paper and found this elemental XPS analysis of an unmodified microscope glass slide surface. C (1s): 17.7% Si (2p): 28.47% O (1s): 53.83% It seems strange for a piece of normal ...
77
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4answers
17k views

Is it true that heavy water is not blue?

I believe I saw this claim somewhere on the internet a long time ago. Specifically, it was claimed that the difference could be observed by filling one long, straight tube with light water and one ...
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2answers
456 views

What is the difference between quantities reported as optical rotation and circular birefringence?

Optical activity gets complicated quickly and the following question is intended to avoid threshold confusion. The linked lecture note* seems very accessible to me and Table 10.6 in particular is ...
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0answers
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Why do electronegative heteroatoms increase C=O stretching frequency (bond strength)

Why does a more electronegative heteroatom (i.e. $\ce{Cl}$ or $\ce{O}$) increase the stretching frequency of a carbonyl? I'd suspect it's that they donate their lone pairs and we end up with a ...
2
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0answers
223 views

Differences in Novichok agent mass spectra

As we have all heard, in 2018, a series of poisonings with a nerve agent alleged to be of the Novichok series was carried out on British soil. It is claimed that the agent used was A-234. However, a ...
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1answer
42k views

What is the effect of conjugation of a carbonyl group in IR spectroscopy?

Doing an exchange term so I've missed some classes that the others have attended, and unfortunately we're getting contradictionary explanations, so I thought I'd try and ask you. Would be extremely ...
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0answers
32 views

Deriving the absorption coefficient from state transitions

This source states that the absorption coefficient $\gamma$ is proportional to the difference in particle number density $\Delta n$ per unit volume between the initial and the final rotational state ...
2
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1answer
38 views

On the detection of molecules in electrospray ionisation (ESI)

Of the ESI spectra that I have encountered, positive & negative mode, the detected species always have charge (positive or negative) corresponding to the charge mode that the machine is in. Is it ...
2
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1answer
620 views

Predicting isotope patterns in mass spectrometry

Imagine you have a mixture of $\ce{^1H}$, $\ce{^2H}$ and $\ce{^3H}$ (hydrogen, deuterium and tritium) present as diatomic molecules and that the numbers of the atoms of the three species are the same. ...
2
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1answer
71 views

Is the XRF spectroscopy equally sensitive for every element?

I am curious whether or not every element can be equally well detected by using X-Ray-fluorescence-spectroscopy. Might there be any contitions or circumstances that make it hard/impossible to detect a ...
0
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1answer
95 views

Why do we see complementary colors in UV/Vis Spectroscopy? [closed]

From what I read, a compound that absorbs visible light will produce a complementary color (using the color wheel), that can be seen. Why is this the case? Is it because, for example, if a molecule ...
2
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0answers
64 views

How is the ΔL = ±1 selection rule derived?

I understand there are selection rules in spectroscopy and quantum mechanics which governs whether a transition happens or not. For example, in atomic spectroscopy, the total orbital angular momentum ...
5
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2answers
97 views

Why are excess nuclei required to produce an NMR signal?

In NMR, an excess population of nuclei is required to produce a signal. If saturation is achieved (same number of nuclei in the α and β states) no net signal can be produced. A signal is produced when ...
-1
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1answer
36 views

Converting Raman Spectra to Infrared Spectra [closed]

I have data for detecting a substance using Raman spectra, but in production, I plan to be using a visible & near-infrared spectrometer. Would it be possible for me to convert from the Raman ...
0
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0answers
93 views

Why does sp2 hybridization result in a greater chemical shift in carbon NMR?

Carbon NMR has a very wide chemical shift range. This is attributed to the relative proximity of electron-withdrawing groups (1-2 bonds separation) compared to proton NMR (2-3 bonds separation) along ...
7
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1answer
89 views

Product operator analysis for CHn groups in HSQC and HMQC

I'm taking and advanced NMR course this semester and we are learning about product operator formalism. I have a homework where I'm supposed to apply this formalism to an HSQC and HMQC experiment. The ...
-1
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1answer
60 views

absorption spectrum of hydrogen atom [closed]

In absorption spectrum of hydrogen atom, only one electron is present in its one atom which is in ground state, so it means that all electrons can only absorb energy of photon of wavelength which lies ...
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0answers
25 views

Explaining allene IR stretching frequency

So I was comparing the IR stretch frequency of ethyne, ethene and allene. Of course triple bond is stiffer than double bond so ethyne has a higher stretch frequency. The problem then is where allene ...
7
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2answers
180 views

Open resource for spectroscopic raw data

Is anyone aware of reliable resources (ideally public) which allow the user to download the raw spectroscopic data such as infrared spectrum of small organic molecules, or rotational spectrum of HCl/...
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1answer
1k views

Deducing compounds from spectroscopic data for isomers of formula C4H8O

Here's the problem: I already know the $\pu{3600 cm-1}$ line indicates the $\ce{-OH}$ group and the $\pu{1640 cm-1}$ line indicates the $\ce{C}$-double-bond-$\ce{C}$ alkene. From the $\ce{^13C}$ ...
3
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1answer
627 views

Determination of structure by 13C and 1H NMR spectroscopy

I'm trying to interpret a $\ce{^{13}C}$-NMR and $\ce{^1H}$-NMR spectrum. So far, I've decided that $\ce{CH3-C}$, $\ce{CH2-CH3}$ and $\ce{CH-CH}$ exist in the structure. I'm not sure but I guess there ...
4
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1answer
176 views

NMR and pseudorotation

I think it has something to do with the fact that at high temperature it interconverts and so all the coupling constants are the same hence quintet but at lower temperatures the frequency of the ...
0
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1answer
54 views

How to perform IR spectroscopy on silica particles at various relative humidities when they are passed through a tube using pressurized air? [closed]

Surface bonds of silica particles are susceptible to humidity and frequently change between silanol and siloxane with changing RH. I want to measure how these surface bonds change with the humidity ...
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0answers
24 views

HNMR spectroscopy mono-carboxylated acid

During lab, I have done following reaction: I did HNMR of the product, to be certain if the product really was formed. The HNMR gave following results: And looked like this: So my question is: has ...
6
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2answers
254 views

Visible Light Spectrophotometer Recommendations

I’m looking into purchasing a cheap uv-vis spectrophotometer but am not affiliated with an institution at the moment given the whole COVID 19 situation. Are there any good recommendations for cheap ...
2
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0answers
30 views

Why is the transition (0,0,0) -> (1,0,1) observed in a gas phase IR spectrum of CO2?

Let ($v_1$,$v_2$,$v_3$) denote the vibrational state of $CO_2$. Why is the transition $(0,0,0)\rightarrow (1,0,1)$ observed when the trasition $(0,0,0)\rightarrow(1,0,0)$ (asymmetric stretch) is not ...
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0answers
30 views

Temperature dependence of emission lines from gases, for example, neon

Emission lines from Ne are frequently used as wavelength standards in spectroscopy. Reading around Wikipedia, I found about the Paschen law regarding the voltage required to start a discharge. My ...
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1answer
52 views

How to calculate the emission wavelength of a substance? [closed]

A light photon (700nm) gets absorbed by a substance*, this substance than emits the light photo. How to find out the wavelength emitted by this light photon? *substance can be anything, I've just ...
2
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0answers
21 views

Vibrational modes in BiOCl

These are the vibrational modes in BiOCl. I'm trying to account for the each mode, and where in the spectrum you would find such mode. And I found out that at 1400 cm-1 you have asymmetric stretch of ...
0
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1answer
38 views

Can a spectrometer be used to figure out spice ratios in a sauce?

There is a really good sauce that a local restaurant makes. I have had trouble recreating it, but have gotten somewhat close. I had the following idea: I could take an "image" of the sauce's color ...
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0answers
20 views

Change in chemical shift of geminal protons in the absence of conformational interconversions

In this post I would like to address a question regarding the chemical shifts of protons which are part of the same chemical environment. It is a known fact that they are not going to split each other ...
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0answers
25 views

EDS of BiOCl (Conductivity)

For EDS mode of SEM, would you need to create a conductive path to ground for a BiOCl sample material. I have researched and found that gold and carbon can be used for such purposes, but I thought ...
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0answers
26 views

EDS analysing the elemental composition

Just wondering if I'm interpreting this correctly. So in SEM, and particularly the EDS mode, the beam irradiation refers to the beam irradiation from the thermionic emission gun. This paper measures ...
2
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0answers
104 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
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1answer
59 views

laser diode problem [closed]

I'm a student studying chemistry, i'm working with diode laser to look at emission spectra for certain complexes. i'm using integrating sphere as my setup, when i use the 405nm diode laser output of 4....
-1
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2answers
89 views

Why does the absorbance of Ca decrease in the presence of certain metals?

I'm trying to find a reason for an experimental observation, I noticed that when the absorbance of $\ce{Ca}$ is measured with FAS(flame atomic spectroscopy) that it decreases when metals such as $\ce{...
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0answers
32 views

What is the best way to go about matching proton-NMR spectra to molecules?

I've attatched an example question. I have already solved this one, I'm wondering about what, in your experience, is the most time-efficient way of approaching a question like this one. I can solve ...
8
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1answer
249 views

Empirical Evidence and Assignment of Orbital Energies (Electron Filling)

I see a lot of questions on electron configurations from students at various levels here. Students mechanically remember how to fill orbitals and sorry to say many teachers do the same. Not a single ...
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0answers
60 views

Term symbols for excited nitrogen (2s2p^4 configuration)

Looking at the NIST levels listing for neutral nitrogen atom, one of the excited configuration is $2s2p^4$ configuration. https://physics.nist.gov/cgi-bin/ASD/energy1.pl?encodedlist=XXT2&de=0&...
5
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2answers
350 views

Can all NMR spectrometers perform special techniques such as COSY, NOESY, HETCOR,..? [closed]

Do you need special spectrometers for: probing nuclei other than hydrogen or carbon? performing 2D spectroscopy such as COSY, NOESY, HETCOR, HSQC,.. Or are these techniques usually available on ...
2
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1answer
44 views

Do the spectra of compound materials combine linearly with respect to the ratios of the constituent compound spectra?

My question stems from reading this article on the FTIR spectrum of oil that has been mixed with various contaminants. If one has the spectrum for the original uncontaminated oil and the spectrum for ...
0
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1answer
50 views

Why do certain signals in proton NMR experience extensive splitting despite only having 1 neighbour?

I came across the compound 3-methylpentan-2-ol. Looking at its proton NMR spectra, it seems there is a lot of splitting for the signal at 4 ppm. I'm assuming that the 4 ppm represents the proton in ...
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0answers
66 views

Effect of ionization on dipole moment

Suppose we have a non-dipolar molecule such as carbon dioxide. If carbon dioxide is ionized by some means in the gas-phase, will it develop a dipole moment? I am asking with reference to microwave ...
4
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1answer
68 views

What exchange timescales are needed to cause decoupling in NMR?

I'll try to explain the source of my confusion as clear as possible: (*) The methyl protons in toluene are decoupled because the C-C bond between the methyl group and benzene allows very fast ...
19
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3answers
2k views

Modern open-source tools for simulation of NMR spectra

I am interested in predicting the NMR spectrum of small organic compounds. It doesn't matter to me if the prediction is very accurate. I'll eventually be comparing the prediction to experimental ...

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