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Title: Conformational explosion: Understanding the complexity of short chain para -dialkylbenzene potential energy surfaces

Journal Article · · Journal of Chemical Physics
DOI:https://doi.org/10.1063/1.5029373· OSTI ID:1512948
 [1]; ORCiD logo [1]; ORCiD logo [1]
  1. Purdue Univ., West Lafayette, IN (United States)
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The single-conformation ultraviolet and infrared spectroscopy of three short-chain para-dialkylbenzenes (para-diethylbenzene, para-dipropylbenzene, and para-dibutylbenzene) is reported for the jet-cooled, isolated molecules. The present study builds off previous work on single-chain n-alkylbenzenes, where an anharmonic local mode Hamiltonian method was developed to account for stretch-bend Fermi resonance in the alkyl CH stretch region [D. P. Tabor et al., J. Chem. Phys. 144, 224310 (2016)]. The jet-cooled molecules are interrogated using laser-induced fluorescence (LIF) excitation, fluorescence dip infrared spectroscopy, and dispersed fluorescence. The LIF spectra in the S1 ← S0 origin region show a dramatic increase in the number of resolved transitions with increasing length of the alkyl chains, reflecting an explosion in the number of unique low-energy conformations formed when two independent alkyl chains are present. Since the barriers to isomerization of the alkyl chain are similar in size, this results in an “egg carton” shaped potential energy surface. A combination of electronic frequency shift and alkyl CH stretch infrared spectra is used to generate a consistent set of conformational assignments. Using these experimental techniques in conjunction with computational methods, subsets of origin transitions in the LIF excitation spectrum can be classified into different conformational families. Two conformations are resolved in para-diethylbenzene, seven in para-dipropylbenzene, and about nineteen in para-dibutylbenzene. These chains are largely independent of each other as there are no new single-chain conformations induced by the presence of a second chain. A cursory LIF excitation scan of para-dioctylbenzene shows a broad congested spectrum at frequencies consistent with interactions of alkyl chains with the phenyl π cloud

Research Organization:
Purdue Univ., West Lafayette, IN (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
Grant/Contract Number:
FG02-96ER14656
OSTI ID:
1512948
Alternate ID(s):
OSTI ID: 1436560
Journal Information:
Journal of Chemical Physics, Vol. 148, Issue 18; ISSN 0021-9606
Publisher:
American Institute of Physics (AIP)Copyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 2 works
Citation information provided by
Web of Science

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journal January 1997

Cited By (1)

Broadband rotational spectroscopy of trans 3-pentenenitrile and 4-pentenenitrile journal January 2019

Figures / Tables (11)

FIG. 1(p. 3)figure FIG. 1
FIG. 2(p. 4)figure FIG. 2
TABLE I(p. 5)table TABLE I
FIG. 3(p. 6)figure FIG. 3
TABLE II(p. 7)table TABLE II
FIG. 4(p. 8)figure FIG. 4
FIG. 5(p. 9)figure FIG. 5
FIG. 6(p. 10)figure FIG. 6
FIG. 7(p. 11)figure FIG. 7
FIG. 8(p. 12)figure FIG. 8
FIG. 9(p. 13)figure FIG. 9

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