Excited State Dynamics of γ-Crotonolactone: Resonance Raman Spectroscopy and Complete Active Space Self-consistent Field(CASSCF) Study†

doi:10.7503/cjcu20150226

Abstract

Abstract:

The structural dynamics and decay mechanisms of γ-crotonolactone in the light-absorbing S₂ excited states were studied by resonance Raman spectroscopy and complete active space self-consistent field(CASSCF) computations. The electronic spectra assignments and the vibrational assignments were done on the basis of the density-functional theory computations and the results of corresponding spectra. The resonance Raman spectra at four excitation wavelength which covered A-band were obtained. CASSCF method was carried out to determine the minimal excitation energies and excited geometries of S_1,min, S_2,min, T_1,min, T_2,min, T_3,min, as well as some conical intersection points. The relation between the structures of excited state $S 2, min$ as well as internal conversion point CI(S₂/S₁) and the intensity mode of resonance Raman spectra was studied. The efficiency of various intersystem crossing is evaluated on the basis of the El-Sayed’s rule, and two major decay channels from S_2,FC to ground state S₀ were proposed. One is the internal conversion channel and the other is the intersystem crossing channel.

Key words: γ-Crotonolactone, Resonance Raman spectrum, Complete active space self-consistent field(CASSCF) computation, Structural dynamics, Non-adiabatic dynamics, Internal conversion, Intersystem crossing

CLC Number:

O641

TrendMD:

OUYANG Bing, XUE Jiadan, ZHENG Xuming. Excited State Dynamics of γ-Crotonolactone: Resonance Raman Spectroscopy and Complete Active Space Self-consistent Field(CASSCF) Study^†[J]. Chem. J. Chinese Universities, 2015, 36(10): 1995.

Figures/Tables 8

Fig.1 UV spectra of γ-crotonolactone in acetonitrile(a) and methanol(b)

Fig.2 Molecular orbitals associated with the electronic transitions

Table 1 Calculated electronic transition energies(ΔE), molecular orbitals and oscillator strengths(f) of γ-crotonolactone

State(C_s)	Orbital	Character	λ/nm(ΔE/eV)		f
State(C_s)	Orbital	Character	Calcd.	Expt.	Calcd.	Expt.^†
S₁(A″)	22→23(0.70)	n_H→ $π L *$	246(5.04)		0
S₂(A')	21→23(0.63)+20→23(-0.29)	π_H-1→ $π L $ +π_H-2→ $π L $	197(6.29)	201	0.2553	0.2784
S₃(A')	20→23(0.64)+21→23(0.28)	π_H-2→ $π L $ +π_H-1→ $π L $	186(6.67)		0.0884

Table 1 Calculated electronic transition energies(ΔE), molecular orbitals and oscillator strengths(f) of γ-crotonolactone

State(C_s)	Orbital	Character	λ/nm(ΔE/eV)		f
State(C_s)	Orbital	Character	Calcd.	Expt.	Calcd.	Expt.^†
S₁(A″)	22→23(0.70)	n_H→ $π L *$	246(5.04)		0
S₂(A')	21→23(0.63)+20→23(-0.29)	π_H-1→ $π L $ +π_H-2→ $π L $	197(6.29)	201	0.2553	0.2784
S₃(A')	20→23(0.64)+21→23(0.28)	π_H-2→ $π L $ +π_H-1→ $π L $	186(6.67)		0.0884

Fig.3 Overall views of the resonance Raman spectra of γ-crotonolactone in acetonitrile(A) and methanol(B)* Labels the solvent subtraction artifacts. a. 204.2 nm; b. 208.8 nm; c. 217.8 nm; d. 228.7 nm.

Fig.4 Enlarged view of the 204.2 nm resonance Raman spectra of γ-crotonolactone in methanol# Marks residual uncertain laser lines.

Table 2 Energies and geometries parameters computed by CASSCF(6,5)/6-31g(d)

State	ΔE/(kJ·mol^-1)(eV)	d_C2—C3/nm	$d C 3 C 4$ /nm	$d C 2 O 6$ /nm	∠ $O 6 C 2 — C 3 C 4$ /(°)
S₀	0	0.1484	0.1335	0.1189	180.0
S_1,FC	510(5.29)
S_1,min(nπ^*)	393(4.07)	0.1355	0.1421	0.1344	-176.0
Δ[S_1,min-S₀]		-0.0129	+0.0086	+0.0155	$4.0$
S_2,FC	753(7.83)
S_2,min(ππ^*)	615(6.38)	0.1387	0.1489	0.1345	-176.2
Δ[S_2,min-S₀]		-0.0097	+0.0154	+0.0156	$3.8$
T_1,min(1)(ππ^*)	309(3.22)	0.1468	0.1495	0.1193	173.4
T_1,min(2)(ππ^*)	380(3.96)	0.1365	0.1.408	0.1341	-170.5
T_2,min(nπ^*)	456(4.73)	0.1332	0.1449	0.1328	-175.2
T_3,min(ππ^*)	498(5.16)	0.1469	0.1321	0.1404	-135.6
CI(S₁/S₀)	556(5.78)	0.1473	0.1319	0.1608	-90.0
CI(S₂/S₁)	690(7.16)	0.1492	0.1428	0.1348	154.5
Δ[CI(S₂/S₁)-S₀]		+0.0008	+0.0093	+0.0159	$25.5$
CI(T₃/T₂)	682(7.06)	0.1487	0.1434	0.1335	152.0
CI(T₂/T₁)(1)	486(4.86)	0.1325	0.1470	0.1331	-176.8
CI(T₂/T₁)(2)	426(4.41)	0.1325	0.1469	0.1331	-176.9
ISC(S₀/T₁)	326(3.39)	0.1501	0.1482	0.1187	158.4
ISC[S₁/T₁(1)]	397(4.03)	0.1358	0.1400	0.1359	-176.3
ISC[S₁/T₁(2)]	389(4.04)	0.1360	0.1413	0.1343	180.0
ISC(S₂/T₃)	644(6.70)	0.1433	0.1500	0.1341	117.2

Table 2 Energies and geometries parameters computed by CASSCF(6,5)/6-31g(d)

State	ΔE/(kJ·mol^-1)(eV)	d_C2—C3/nm	$d C 3 C 4$ /nm	$d C 2 O 6$ /nm	∠ $O 6 C 2 — C 3 C 4$ /(°)
S₀	0	0.1484	0.1335	0.1189	180.0
S_1,FC	510(5.29)
S_1,min(nπ^*)	393(4.07)	0.1355	0.1421	0.1344	-176.0
Δ[S_1,min-S₀]		-0.0129	+0.0086	+0.0155	$4.0$
S_2,FC	753(7.83)
S_2,min(ππ^*)	615(6.38)	0.1387	0.1489	0.1345	-176.2
Δ[S_2,min-S₀]		-0.0097	+0.0154	+0.0156	$3.8$
T_1,min(1)(ππ^*)	309(3.22)	0.1468	0.1495	0.1193	173.4
T_1,min(2)(ππ^*)	380(3.96)	0.1365	0.1.408	0.1341	-170.5
T_2,min(nπ^*)	456(4.73)	0.1332	0.1449	0.1328	-175.2
T_3,min(ππ^*)	498(5.16)	0.1469	0.1321	0.1404	-135.6
CI(S₁/S₀)	556(5.78)	0.1473	0.1319	0.1608	-90.0
CI(S₂/S₁)	690(7.16)	0.1492	0.1428	0.1348	154.5
Δ[CI(S₂/S₁)-S₀]		+0.0008	+0.0093	+0.0159	$25.5$
CI(T₃/T₂)	682(7.06)	0.1487	0.1434	0.1335	152.0
CI(T₂/T₁)(1)	486(4.86)	0.1325	0.1470	0.1331	-176.8
CI(T₂/T₁)(2)	426(4.41)	0.1325	0.1469	0.1331	-176.9
ISC(S₀/T₁)	326(3.39)	0.1501	0.1482	0.1187	158.4
ISC[S₁/T₁(1)]	397(4.03)	0.1358	0.1400	0.1359	-176.3
ISC[S₁/T₁(2)]	389(4.04)	0.1360	0.1413	0.1343	180.0
ISC(S₂/T₃)	644(6.70)	0.1433	0.1500	0.1341	117.2

Fig.5 Optimized geometry structures of the excited states and the conical intersection points ofγ-crotonolactone by CASSCF(6,5)/6-31g(d)

Fig.6 Schematic diagram of the major decay channels of γ-crotonolactone initiated from S2,FC

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