Development of models for quantum dynamical simulations of photo-excited molecules. Application to the ππ*/nπ* internal conversion in thymine

This work illustrates the theoretical modeling and the results of quantum and mixed quantum-classical dynamical simulations of the ππ* -> nπ* internal conversion in the thymine molecule. The importance of this process in the fields of photochemistry and photobiology is related to the photostability of nucleic acids. In fact, nucleobases strongly absorb UV light, undergoing electronic transitions to excited reactive ππ* states, leading to potentially mutagenic effects. However, time-resolved experiments show that the ππ* state is depopulated in an ultrafast (< 500 fs) time scale, and the relevance, in pyrimidine nucleobases, of its deactivation, via an internal conversion to a nπ* state, closely lying in energy, is strongly debated in literature. For the purposes of this work, a novel methodology for the quantum dynamical study of semirigid photoexcited nonadiabatic (i. e. with electronic states close in energy) chromophores is illustrated. As an original result, it is proven that, if the excited state Potential Energy Surfaces (PES) are described within the harmonic approximation, it is possible to find effective coordinates partitioned into blocks, defining a hierarchical sequence of Hamiltonians to compute quantum dynamics, where the members of the hierarchy depend on a growing number of coordinates. A procedure is presented to build up this sequence of Hamiltonians, that has the property that the larger the number of effective coordinates, the longer the time scale to which the dynamics is reproduced exactly. This is a new approach, generally applicable to the study of the excited state dynamics of semirigid molecular systems, and improves a pre-existing hierarchical model for harmonic PESs, valid only in the limit where the excited state has the same frequencies and normal modes of the ground state (in practice, quite 'rigid' assumptions, even according to the chemical intuition). The procedure is applied here to the simulation of the ππ*->nπ* excited state transfer in thymine, exploiting different levels of accuracy for constructing the quadratic PESs of the excited states involved in the dynamics, and discussing the differences between such different approaches. The results show that the transfer is effective (80%) and occurs in a time scale of <100 fs; therefore the nπ* state is involved in the dynamics from the very beginning. The nonadiabatic absorption spectra are also computed and compared with experimental measurements. Moreover, the convergence of the predicted population transfer and the absorption spectra, with respect to the number of coordinates included is tested and proved, so that the theoretical methodology developed reveals to be very satisfactory

The Ursinus Weekly, February 20, 1969

Excavation begun on lab facilities • Byerly discusses U.C. status for Phi Beta Kappa • Emig turns back Sayare challenge; Novak, Rozycka win in close V.P. contests • SFARC to conduct student drinking poll • Parking regulations • UC Arts Festival opens on March 7 • Only 125 attend winter IF dance • In memoriam • Kitchen experiment • On applied pressure • Letters to the editor • Forum review: Man-sculpture relationship born of African creations\u27 animism • Editorial: Arts weekend, March 7-9 • St. Andrews Society grants awards for study in Scotland • SFARC considers alcohol, arrangement of rules • U.C. holds bleed-in • Ursinus offers graduate course • Sirens seek Lorelei dates • Print Club sponsors campus print exhibit • Bears fall to Mules after Hopkins win • Hofmaster lone victor in Delaware mauling • Gillespie takes luncheon award • Dickinson studies alternatives to college fraternity system • Contemplationshttps://digitalcommons.ursinus.edu/weekly/1170/thumbnail.jp

Vibrationally resolved two-photon electronic spectra including vibrational pre-excitation:Theory and application to VIPER spectroscopy with two-photon excitation

Following up on our previous work on vibrationally resolved electronic absorption spectra including the effect of vibrational pre-excitation [J. von Cosel et al., J. Chem. Phys. 147, 164116 (2017)], we present a combined theoretical and experimental study of two-photon induced vibronic transitions in polyatomic molecules that are probed in the Vibrationally Promoted Electronic Resonance experiment using two-photon excitation (2P-VIPER). In order to compute vibronic spectra, we employ time-independent and time-dependent methods based on the evaluation of Franck-Condon overlap integrals and Fourier transformation of time-domain correlation functions, respectively. The time-independent approach uses a generalized version of the FCclasses method, while the time-dependent approach relies on the analytical evaluation of Gaussian moments within the harmonic approximation including Duschinsky rotation effects. For the Coumarin 6 dye, two-dimensional 2P-VIPER experiments involving excitation to the lowest-lying singlet excited state S1 are presented and compared with corresponding one-photon (1P)-VIPER spectra. In both cases, coumarin ring modes and a CO stretch mode show VIPER activity, albeit with different relative intensities. Selective pre-excitation of these modes leads to a pronounced redshift of the low-frequency edge of the electronic absorption spectrum, which is a prerequisite for the VIPER experiment. Theoretical analysis underscores the role of interference between Franck-Condon and Herzberg-Teller effects in the two-photon experiment, which is at the root of the observed intensity distribution

The Ursinus Weekly, October 31, 1968

Evaluation favorable; Provincialism assailed • Nixon overwhelms Humphrey; Rightward trend reflected • Founders\u27 Day honors alumni; Honorary degrees conferred • Secret society members elected • Placement Office offers services to \u2769 graduates • Barbara Bruzgo crowned \u2768 Homecoming Queen • Editorial: Activities chaos • Grand Dragon at U.C.; Klan views stated • Grape conspiracy • Letters to the editor • Formation of a fourth party • Editorial: Literary dilemma • Arts forum features four faculty speakers • Opinion: Sulphuric acid + gas • Bears rip Garnet in Homecoming game after humiliating defeat at Muhlenberg • Gillespie and Gane selected as co-captains • Soccer team defeated by Mules and Delaware as Grau is injured • Inside track: And Drexel makes eighteen • Bearettes and West Chester battle here next Thursday • Magicians, Homecoming and R. J. Whatley • Flowers are still undefeated as I.T.F.L. enters fourth week; Beta Sig upsets Sig Rho, 12-7 • Del Valley\u27s QB is man to watch • Hockey team destroys opponents; Cash and Landis star, score 13 • Greek gleaningshttps://digitalcommons.ursinus.edu/weekly/1165/thumbnail.jp

The Ursinus Weekly, December 2, 1968

Arts Forum held; 4 foreign students featured on panel • Board OKs student members on committees; Student Senate endorses SFARC resolution • Camino real scheduled for December 6th • Mandrake concert is hit; Rock group shows profit • Editorial: Our play; The larger issue • Letters to the editor • Tradition vs. change • Herberg sees anomic moral crisis; Fun morality termed other directed • SFARC minutes • Opinion: Speaker fails to prove dilemma • Freeland Hall: Don\u27t let it be forgot • Senior looks at Freeland: Can Library replace Freeland\u27s primacy? • Search into history substantiates claim of second oldest graduate that Freeland was everything • Instructor asks what do students really want? • Now is the time to unite • WRUC increases wattage to allow greater service • USGA discusses Black Alliance • Students to decide on two government proposals • Pratt art show opens at Ursinus • PNE Folk Fest held; U.C. talent featured • U.C. sponsors Career Days • Howard honored for achievements • Gurzynski\u27s men win title; Albert leads UC to championship • Soccer team edges LaSalle after losing to Haverford • Flowers win intramural crown with 6-0 victory over Sig Rho • Whatley lauds squad; predicts progress • Bears destroy Haverford; Shuman wins Maxwell Award • All Stars will visit Glassboro • Greek gleaningshttps://digitalcommons.ursinus.edu/weekly/1167/thumbnail.jp

The Ursinus Weekly, March 6, 1969

Officers inducted; Emig emphasizes new responsibility • American dream, brotherhood highlight Festival of the Arts • USGA officers interviewed; Communication gap stressed • Placement interviews scheduled • 200 attend Lorelei; Fischer crowned king • Semi-formal ball highlights junior-senior weekend • Editorial: Potpourri - Or, Could this ever happen here? • State set to punish protestors; Laws threaten civil liberties • Letters to the editor • Remark • Lantern literary lapse termed titanic bomb • Staying out of uniform: A practical guide for the Ursinus male, part I • Whose risk? • Columnist proposes solution to UC\u27s dearth of black students • Albright draws Fifth Dimension • Racism symposium set for March 20 with Lincoln Univ. • Dorm lounges opened; Slacks rule slackened • Rice discusses status for Phi Beta Kappa • Ursinus grapplers rally to win over Drexel, 22-13 • New gym complex to include pool • Carson paces Bearettes over Gettysburg • Badminton team wins six in row • Trackmen run at Swarthmore and Delaware • Gillespie hits 37 points to lead Bears over Swarthmore in finale • Girl swimmers win over Penn and Elizabethtown • Junior varsity hoopmen finish with 11-6 record • Dickinson frat system defended • UC celebrates centennial with unique innovation • Forum features Howellhttps://digitalcommons.ursinus.edu/weekly/1171/thumbnail.jp

The Ursinus Weekly, December 19, 1968

Messiah presented by Ursinus choir; Performances draw SRO audiences • Frat system & houses favored by students; 12% thumbs down! • 878 enrolled in U.C. Evening School • YM-YWCA supports SFARC investigation • Editorial: Activities chaos rolls on • Drama in real life • Student long-term planning committee report • Letters to the editor • Flu strikes East; U.C. still healthy • A memory with pillars • A Christmas story • Murmurs from within • Exchange • Faculty portrait: Mr. Sharp; Hangup on social problems overshadows intellectual quest • UC pranks: They\u27re all in good fun; Was Freeland ghost really Dr. Helfferich? • Many of greatest pranks took place in Chapel • Doctors Yost and Parsons recall Ursinus shenanigans of yesteryear; Boycotts, pigs, moths make hits • Protheatre makes hit debut in New Theatre production • Opinion: Open letter to Byron Jackson • Greek gleanings • Winning doesn\u27t count but being clean-shaven does • Snellbelles open against Moravian • Outweighed, but still fighting • Bears to face area teams, will see many super sophs • Women\u27s wrestling wound-up • Quiet revolution topic of discussion • Dr. Lewis announces $1000 trust fund • Blacks\u27 non-recognition: one topic for USGAhttps://digitalcommons.ursinus.edu/weekly/1168/thumbnail.jp

The Ursinus Weekly, October 17, 1968

Fraternities hopeful as Homecoming approaches; Reigning Queen to be selected in regal runoff • Student teachers gain experience • Frosh elect officers; President sets goals • Curtain Club changes name to ProTheatre • Ryan Brothers highlights UC folk concert • Editorial: A matter of concern • On love and hate • Coke culture to stay Glenesk tells Forum • Letters • Dr. Byerly raps Greeks; Calls rushing degrading • Freshmen induction: Questionable success • Intruders in concert • Exchange column • Another view: Ursinus change • Opinion: Political commentary • Expansion necessitates dormitory renovations • SFARC minutes • Ursinus students to participate in TV program • U.C. students speak at pre-med meeting • Parents feted at gala event • Bear Gridders fall to Johns Hopkins and Lebanon Valley; Streaking Harriers extend undefeated string to fifteen • Grau predicts comeback for soccer squad • A little bit about everything or not much about anything • UC hockey team edges Penn, 2-1 as Cash scores decisive goal • Ursinus must stop Muhlenberg offense • Sig Rho and Apes are on top in I.T. fraternity division; Flowers down Day Study, 13-6 • Greek gleaningshttps://digitalcommons.ursinus.edu/weekly/1164/thumbnail.jp