Spectroscopy Flashcards
Says that the energy of electrons in atoms and molecules are quantized in specific allowed energy levels
quantum theory
Electrons, ___ or ___ are excited to higher electronic states by __ or ____ and then give off ___ as the electrons relax back from higher energy states to lower energy states. The difference between two of these allowed energy levels can be measured when a system ___ or ___ these photons of electromagnetic radiation
atoms, ions, heat, light, photons, absorbs, emits
Light consists of packets of photons of various wavelengths that have no ___, are ____ ___, have a ___ field, and have an ___ field
mass, pure energy, magnetic, electric
The electrons generate a magnetic field because it ___ and carries a ___. When there is an external magnetic field, the electron can orient its spin __ or ___ that field
spins, charge, with, against
All molecules have a series of _____ modes whose motion and hence __ are quantized. Complicated molecules may vibrate in a number of different ____. Vibrations can be excited by the absorption of electromagnetic radiation in the ____ region.
vibrational, energies, modes, IR
Typical energies for vibrational excitation are _____and the frequency of radiation absorbed should be ____
10E-20 - 10E-10, 10E13-10E14
The __ ___ ___ says that the electric dipole moment of the molecule must change during the vibration. ___ ____ are IR inactive since there can be no dipole moment change during their one and only __ ___, thus their vibrations do not absorb of generate radiation. ___ ___ will be IR active
gross selection rule, homonuclear diatomics, stretch mode, heteronuclear diatomics
The __ ___ __ ___ states that the change in vibrational energy between two states is always equal to ___. in other words, it vibrates one ___ higher when the photons have just the right amount of energy and the molecule absorbs ____
quantum mechanical selection rule, +1, unit, light
At room temperature, almost all molecules will be in their vibrational ___ ___, so the main spectral transition upon photon absorption will be from ___ to _____
ground state, v=1, v=0
For a molecule of N atoms, there are ____ vibrational. modes for polyatomic molecules and ____ modes for linear polyatomic molecules
3N-6, 3N-5
In an IR spectrum various absorption peaks correspond to the __, ___, ___ and ___ vibrational modes.
stretching, bending, rocking, wagging
Vibrations that don’t involve ____ have lower energy transitions and are found in the region below _____cm^-1. This region is called the __ ___ because it contains many distinctive peaks that can be used to identify ____, and contains all possible _____ vibrations of a molecule
stretching, 1500, fingerprint region, unknowns, bending
IR spectroscopy is used for the identification of __ ___ before NMR was invented, __ __ determination in organic and inorganic synthesis, in __ ___ where molecules are in the gas phase, in physical chemistry for determining __ ____, and for detecting very ___ amounts of material
molecular structure, functional group, atmospheric spectroscopy, bond strengths, small
Are _____cm^1 peak in an IR spectrum is indicative of a benzene ring
900-600
In UV/VIS spectroscopy, ___ are excited usually from a -__ or ____ molecular orbital to a nearby empty _______ orbital. The most probable electronic transitions occur from ___ to the ____.
electrons, bonding, nonbonding, antibonding, HOMO, LUMO
The photon energy wavelengths for the UV region is _____, and ___ for the VIS region
200-400, 400-700
The colour that we see are the photon frequencies that are ___ ___
not absorbed
The intensity of absorption is given by the __ __ ___
beer lambert law
UV/Vis show more _____ absorption bands compared to IR spectra. This is because electronic excitation happens much ___ than vibrations of atoms in the molecule. In a ___ transitions can be distinguished and show up as distinct absorption lines, while in liquids and solids, the transitions are mixed up, making it harder to distinguish ___ ____.
broad, faster, gas, individual vibrations
The ____ ____ ____says that faster transitions mean that nuclei do not respond fast enough for its ___ to change (in contrast to IR transitions where the geometry does change)
franck-condon principle, geometry
Most ___ ___ do not have colour. Organic molecules with ___ __ __ absorb light in the UV region. When conjugated double bonds form ___ or longer chains, the difference between the energy level of the HOMO and LUMO decreases. This results in the energy needed for electron transitions to ___, resulting in ___ wavelengths of absorbed light. This results in a switch from the UV to the ___ spectrum, making the molecule appear coloured
organic molecules, conjugated double bonds, 8+ , decrease, longer, vis
UV/VIS spectroscopy is used in ___ _____ __ ___ to examine the separated fractions of a mixture
high performance liquid chromatography
The part of the molecule that gives rise to the UV.VIS electronic absorption
chromophore
In organic chemistry, C-C ____ ____ and extended _____ series of double bonds, ____ ____, isolated ___ groups, and
carbonyls conjugated to extended ____ _____ are the chromophore. In inorganic chemistry, many coloured metal complexes occur for transition metals such as ___, ___, ___ and ___, due to electronic absorption by valence shell ___ electrons into LUMOS
double bonds, conjugated, phenyl rings, carbonyl, pi systems, Ni2+, Fe3+, Cu2+, Ti3+, d
Electronic transitions are usually referred to as
N to pi, N to sigma, Pi to pi, or sigma to sigma
When the UV spectrum is measured for a compound in the ___ phase, ____ fine structure can often be seen in electronic transition bands. Vibrational modes can slightly alter the ___ associated with electronic transitions. If the spectrum is measured in a solution, interaction with the ___ usually broadens the absorption peaks so a less detailed spectrum is obtained.
gas, vibrational, energies, solvent
