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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Which Organic Compound is it based on IR Spectrum(C4H8O2)? [closed]

Was solving a few problems, came through this one, was confused with the isomers of the compound , it would be nice if anyone could tell which compound it is and why?
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64 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 ...
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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 ...
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What can we separate 3-methylcyclopentene and 4-methylcyclopentene by using ¹H NMR?

I write the structures and, I couldn't find any difference between 3-methylcyclopentene and 4-methylcyclopentene since all peaks are equal. Is there something I am missing?
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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 ...
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32 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 ...
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83 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 ...
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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 ...
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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 ...
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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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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 ...
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Open source for atomic spectra raw data

Is anyone aware of a open source atomic spectra database? In particular I am looking for high resolution Na atomic emission which can be downloaded in csv or Excel. I am aware of NIST but I could not ...
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CNT Raman ratio of G band to 2D band?

I believe that the G band (~1600 cm-1) shows the stretching mode of the graphene in a carbon nanotube (e.g. chiral, zigzag, armchair) and the 2D band (~2680 cm-1) shows the number of walls in the CNT. ...
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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 ...
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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 ...
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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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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
32 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 ...
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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 ...
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1answer
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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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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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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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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 ...
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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
52 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....
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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 ...
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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&...
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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 ...
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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 ...
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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 ...
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1answer
48 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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1answer
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Haemoglobin literature spectra does not match

I am studying haemoglobin absorption spectra in its oxygenated and deoxygenated state and I compiled values from different sources including: A PhD thesis by van Assendelft [1], using extinction ...
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51 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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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 ...
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why is the H-NMR chemical shift of methane lower than that for ethane?

If we replace one hydrogen in methane by a methyl group we arrive at ethane. Now we can say: Carbon is more electronegative, and so it withdraws electrons which leads to deshielding. This is why the ...
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Why does peak decoupling occur in H-NMR spectra?

For example, when we analyze the conversion of some chemical compound, certain characteristic areas tend to decrease (ok). However, why can a peak (i.e., one peak) generate smaller peaks (i.e., more ...
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1answer
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Different force constant in ground vs excited state in spectroscopy

The force constant of iodine in the first excited state is $k=41.78$ N/m, and in the ground state it is $170$ N/m. I know that the formula for calculating $k$ is: $$ k= (\frac{ΔE_{vib} *2π}{h})^2 µ$$...
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Enantiomers to diasteroisomers (rotational spectra)

Enantiomers have identical rotational spectrum because their mass distributions are identical. Recently a trick has been introduced in microwave spectroscopy in which a enatiomerically pure gas chiral ...
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373 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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Question about a line from Rosenfeld's paper on optical rotation

There are a lot of papers on optical rotation which cite Rosenfeld's (German) 1928 paper "Quantum mechanical theory of natural optical rotation..." [Quantenmechanische Theorie der naturlichen ...
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1answer
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Beer's law: UV-Vis absorbance values exceeding 2

In classical analytical chemistry, absorbance values in Beer's law can theoretically range from 0 to infinity. As general rule of thumb neither high, nor very low absorbance are used for ...
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Why does Larmor precession occur in NMR?

Larmor precession is the phenomenon that in NMR the spin (and by default also the magnetic dipole moment) of protons does not line up with the applied magnetic field but rather precesses around this ...
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1answer
193 views

How can every atom have unique spectral lines?

Why does every element have unique spectral lines? I have studied that spectral lines help us to identify the properties of an element. This is because after excitation when the excited electron(s) ...
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1answer
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How to find the lifetime of sodium atoms in the 3p using information on the spectral line width?

I am trying to find the lifetime of sodium atoms at the 3p state using the relationship between the spectral linewidth and the uncertainty principle: $$ \Delta E \times \Delta t = h / 4\pi $$ The ...
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Is there an anisotropy factor (g factor) for TDDFT Abs and CD calculations?

Experimentally, anisotropy factor is calculated by dividing the CD spectra by the absorbance spectra multiplying by a factor of 32980 (in order to get a nondimensional quantity) Theoretical ...
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LIF spectrum with laser-coupled levels lines as the strongest

Why, if I excited the OH molecule Q-branch transition, my LIF spectrum (recorded during and after the laser pulse) does not result in only Q line being the most prominent, but also P and R lines with $...
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1answer
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Emission spectra (Be and Mg)

The line says Alkaline metals and their salts impart characteristic colour to an oxidising flame. This is because the heat from the flame excites the outermost orbital electron to higher energy ...
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Interpretation of Carbon-13 NMR Spectra for Chemically Similar Carbon Atoms

I am analyzing the Carbon-13 NMR data from a reaction I will be modifying. There is not NMR data available for the specific compound I am attempting to synthesize; however, the compound I am ...
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In UV photoelectron spectroscopy why are filled orbitals seen at a higher binding energy?

I understand that the partially filled Ni intersects the Fermi level as there is a change from filled to unfilled orbitals. But what is the explanation for the lower binding energy of the filled 3d Cu ...
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How can the formula of WD-40 remain a trade secret?

Wikipedia says WD-40's formula is a trade secret How can it remain a secret today? Can't mass spectrometers, NMR and other equipment be used to determine the structure of the compounds that go ...

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