The electronic absorption spectra of NH 2 and ND 2

1959 ◽  
Vol 251 (1002) ◽  
pp. 553-602 ◽  
Keyword(s):  
Excited State ◽  
Bond Length ◽  
Absorption Spectra ◽  
Flash Photolysis ◽  
Electronic Absorption Spectra ◽  
Interaction Constant ◽  
Bending Vibration ◽  
Vibronic Structure ◽  
Linear Configuration ◽  
Centrifugal Distortion Constants

The absorption spectra of <super>14</super>NH 2 , <super>15</super>NH 2 and <super>14</super>ND 2 have been photographed in the region 3900 to 8300 A with a 21 ft. concave grating spectrograph. The radicals are produced by the flash photolysis of <super>14</super>NH 3 , <super>15</super>NH 3 and <super>14</super>ND 3 respectively. A detailed study of the <super>14</super>NH 2 - <super>15</super>NH 2 isotope shifts suggests that the molecule has a linear configuration in the excited state and that the spectrum consists of a long progression of the bending vibration in this state. These conclusions have been confirmed by detailed rotational and vibrational analyses of the 14NH2 and 14ND2 spectra. The spectra consist of type C bands for which the transition moment is perpendicular to the plane of the molecule. For NH2, sixteen bands of the progression (0, v'%, 0) <- (0, 0, 0) have been identified with v'% — 3, 4, ..., 18. In addition four bands of a subsidiary progression (1, v'2, 0) <- (0, 0, 0) have been found; these bands derive most of their intensity from a Fermi-type resonance between (0, v'2) 0) and (1, v2 —4, 0) levels in the excited state. The interaction constant W nl is 72 + 3 cm <super>-1</super>. For ND 2 , fourteen bands of the principal progression (v2 — 5 to 18) and one band of the subsidiary progression have been identified. The upper state vibration frequencies w?' and (i)' are 3325 cm <super>-1</super> and 622 cm <super>-1</super> for NH 2 and 2520 cm <super>-1</super> and 422 cm <super>-1</super> for ND 2 respectively. The bending frequencies are unusually low ; moreover, the anharmonicities of the bending vibration are unusually large and negative (x22—11.4 cm <super>-1</super> for NH 2 and 8.1 cm <super>-1</super> for ND 2 ). The origin of the system lies in the region o f 10000 cm <super>-1</super>. Ground-state rotational term values have been derived from observed com bination differences; values for the rotational constants Aooo, B'ooo and Cooo and for the centrifugal distortion constants D"A, D"b and D"0 have been determined. The bond lengths and bond angles for NH 2 and ND 2 agree and are 1.024 + 0.005 A and 103° 20' + 30' respectively. Small spin splittings have been observed. In the excited state an unusual type of vibronic structure has been found. Successive levels of the bending vibration consist alternately of 27, d , T, ... and ... vibronic sub-levels with large vibronic splittings. The origins of the vibronic sub-bands may be represented by the formula yf = Vq—GK2, where G is ~ 27 cm -1 for NH 2 and ~ 19 cm <super>-1</super> for ND 2 . The rotational levels show both spin and A-type doubling. No simple formula has been found to fit the energies o f the II, A, 0 and -T rotational levels; the 27 levels fit the formula F(N) = 1) — D N2(N + 1)2, though with a negative value for D . By extrapolating the B values for the 27 levels to = 0 we obtain B'00o = 8.7 8 cm <super>-1</super> for NH 2 and 4.4 1 cm<super>-1</super> for ND 2 . These values are consistent with a linear configuration with a bond length of 0.97 5 A. The significance of this short bond length is discussed. An explanation of the complex vibronic structure is given. The two combining states are both derived from an electronic II state which is split by electronic-vibrational coupling for the reasons advanced by Renner. A detailed correlation diagram is given. A quantitative treatment of this effect by Pople & Longuet-Higgins gives good agreement with the experimental data.

Excited State Polarizability of Some Polycyclic Polyenes

2017 ◽  
Vol 68 (2) ◽  
pp. 307-310 ◽  
Author(s):  
Ana Maria Ciubara ◽  
Andreea Celia Benchea ◽  
Carmen Beatrice Zelinschi ◽  
Dana Ortansa Dorohoi
Keyword(s):  
Excited State ◽  
Absorption Spectra ◽  
Excited States ◽  
Electronic Absorption ◽  
Ground State ◽  
Electronic Absorption Spectra ◽  
Photon Absorption ◽  
Absorption Process ◽  
Polar Solvents ◽  
Molecular Parameters

The electronic absorption spectra of five polycyclic polyenes were recorded in non-polar solvents in order to determine their polarizability in excited states from the strength of the dispersive interactions in their diluted solutions. The bathochromic shifts of p-p* vibronic bands prove the increase of the molecular polarizabilty in the photon absorption process. Some molecular parameters of the analyzed polyenes in their ground state were computed by using the programs from Spartan�14.

scholarly journals Detailed analysis of the vibronic structure of phenetole in its first excited state and ionic ground state

2019 ◽  
Vol 25 (1) ◽  
pp. 142-156 ◽  
Author(s):  
Niklas Helle ◽  
Immo Hintelmann ◽  
Jürgen Grotemeyer
Keyword(s):  
Excited State ◽  
Ground State ◽  
Bending Vibration ◽  
Vibronic Structure ◽  
Td Dft ◽  
First Excited State ◽  
Electronically Excited ◽  
Mati Spectroscopy ◽  
Adiabatic Ionization Energy ◽  
Franck Condon

The vibronic structure of the first electronically excited state S1 and ionic ground state D0 of phenetole has been investigated by means of resonance enhanced multi photon ionization (REMPI) and mass analyzed threshold ionization (MATI) spectroscopy. The vibronic levels were assigned with the aid of quantum chemical calculations at the (TD)DFT level of theory and a multidimensional Franck-Condon approach. The S1 excitation energy of phenetole has been determined to be 36370 ± 4 cm−1 (4.5093 ± 0.0005 eV). The adiabatic ionization energy was determined to be 65665 ± 7 cm−1 (8.1415 ± 0.0008 eV). The vibronic structure has been analyzed whereby the in-plane bending vibration νbend shows high activity in the first excited state but is more pronounced in the ionic ground state. Moreover, a strong Duschinsky rotation effect can be observed for several D0←S1 transitions that causes violations of the Δv = 0 propensity rule.

ABSORPTION SPECTRA OF HCCl AND DCCl

1966 ◽  
Vol 44 (3) ◽  
pp. 525-547 ◽  
Author(s):  
A. J. Merer ◽  
D. N. Travis
Keyword(s):  
Bond Length ◽  
Flash Photolysis ◽  
Energy Levels ◽  
Large Change ◽  
Absorption Bands ◽  
Bending Vibration ◽  
Equilibrium Angle ◽  
Vibrational Levels ◽  
Type C ◽  
Axis Switching

A long progression of absorption bands appearing in the region 5 500–8 200 Å has been observed in the flash photolysis of dibromochloromethane, HCClBr2. Observation of chlorine and deuterium isotope shifts, together with the results of the rotational analyses, have shown that the carrier of the bands is the chloromethylene radical, HCCl.The ground state of HCCl is a 1A′ state in which the molecule has an equilibrium angle of ~103°, a C—H bond length of 1.12 Å, and a C—Cl bond length of 1.69 Å. In the upper state, of character 1A″, unusual patterns of the vibrational and K-type rotational energy levels indicate that the molecule, although bent, has a low barrier to linearity and is easily "straightened" by vibration. The vibrational levels of the upper state may be fitted quite accurately, using a potential function for the bending vibration of the type suggested by Thorson and Nakagawa (1960); our calculations show that the equilibrium angle in the upper state is ~135° and that the top of the barrier lies 2 250 cm−1 above the lowest vibrational level.The large change of angle in the transition causes the appearance of subbands with ΔK = 0 and −2 in addition to those allowed by the strict type-C selection rules. The intensities of the forbidden subbands are well explained by the axis-switching mechanism suggested by Hougen and Watson (1965).

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