Whitley Heather D, DuBois Jonathan L, Whaley K Birgitta
Department of Chemistry and Kenneth S. Pitzer Center for Theoretical Chemistry, University of California, Berkeley, California 94720, USA.
J Chem Phys. 2009 Sep 28;131(12):124514. doi: 10.1063/1.3236386.
Spectral shifts of electronic transitions of tetracene in helium droplets are investigated in a theoretical study of (4)He(N)-tetracene clusters with 1 < or = N < or = 150. Utilizing a pairwise interaction for the S(0) state of tetracene with helium that is extended by semiempirical terms to construct a potential for the S(1) state of tetracene with helium, the spectral shift is calculated from path integral Monte Carlo calculations of the helium equilibrium properties with tetracene in the S(0) and S(1) states at T = 0 and at T = 0.625 K. The calculated spectral shifts are in quantitative agreement with available experimental measurements for small values of N (< or = 8) at T approximately 0.4 K and show qualitative agreement for larger N (10-20). The extrapolated value of the spectral shift in large droplets (N approximately 10(4)) is approximately 90% of the experimentally measured value. We find no evidence of multiple configurations of helium for any cluster size for either the S(0) or S(1) state of tetracene. These results suggest that the observed spectral splitting of electronic transitions of tetracene in large helium droplets is not due to the coexistence of static metastable helium densities, unlike the situation previously analyzed for the phthalocyanine molecule.
在一项针对1≤N≤150的(4)He(N)-并四苯团簇的理论研究中，对并四苯在氦液滴中的电子跃迁光谱位移进行了研究。利用并四苯S(0)态与氦之间的成对相互作用，并通过半经验项进行扩展，以构建并四苯S(1)态与氦的势能，通过路径积分蒙特卡罗计算在T = 0和T = 0.625 K时处于S(0)和S(1)态的并四苯与氦的平衡性质，从而计算光谱位移。计算得到的光谱位移与在T≈0.4 K时N值较小（≤8）的现有实验测量值在数量上一致，并且对于较大的N值（10 - 20）显示出定性一致。大液滴（N≈10⁴）中光谱位移的外推值约为实验测量值的90%。我们没有发现对于并四苯的S(0)态或S(1)态，在任何团簇尺寸下氦存在多种构型的证据。这些结果表明，与之前对酞菁分子分析的情况不同，在大氦液滴中观察到的并四苯电子跃迁光谱分裂并非由于静态亚稳氦密度的共存。
